It is, but the phrase "absent other factors" is convenient. It's upsetting to nearly no one that physically small NFL coaches are rare, yet the development system that produces NFL coaches inhibits the ability of those persons to advance to a head coaching position, despite them being, in theory, equally able to coach. Is that structural inhibition a factor to be absented, or a systemic problem?
(Or are small coaches excluded because they aren't taken seriously on the basis of something they can't help, but which wouldn't inhibit their job performance, excepting the reactions of prejudiced players and staff? We don't consider smallness a racial characteristic, despite its heritability, association with ancestry, and propensity to be met with prejudice, but discrimination because of size where it doesn't matter is the same evil as racism.)
Like most major professional team sports in the US (and Canada in the case of the NBA/MLB/NHL), the coaching ranks of the NFL are made up primarily of former players of that sport. The NFL is actually unique (compared with MLB, the NBA, and the NHL where the majority of coaches/managers are former pros) in that only five of its current coaches had actual professional careers (though two more were replacement players). Nonetheless all but one (Todd Haley of Kansas City) of the current crop of 32 coaches played at least college-level football.
As you would expect, with the exception of kickers, most current and former football players are pretty big guys. A 2005 ESPN article said that at the time the average height of an NFL player was about six feet and the average weight was about 248 pounds. Those height and weight numbers are only increasing as time goes on. This isn't bias against short people for some factor that doesn't affect game play (like skin color), it's basic survival in a sport where an average-sized 5'11'', 199 lb. Defensive Back at speed can hit you with 1600 pounds of force. Tallness also has an advantage in being able to see/throw/catch/jump over and have a longer stride than other players.
Height is also not one of the protected classes in federal anti-discrimination law, while race is.
Furthermore, while shortness is not common in the NFL (though not unheard of), being a minority (especially black) is. It is that disparity between the number of minority players and the lack of minority coaches that the Rooney Rule was established to address, and in that regard it has done remarkably well with there now being 22% black coaches versus where it began in 2003 at 6% (which is where the percentage of minority coaches in college football still remains; and why they are considering a Rooney Rule for college football as well).
So until you can show that there are a largely disproportional number of short players versus short coaches in the NFL, it's a pretty silly argument.
I would suppose that there are two problems: racism and educational imbalance (itself caused largely by racism, both historical and current).
Unlike some other pro sports, the NFL does not allow players to be drafted straight out of high school. They are not required to attend a university, but they do have to wait a minimum of three years from their high school graduation to play in the NFL, and most do choose to pursue a college football career (and education) in order to bulk up, stay in condition, and build experience. Once in college they can be drafted to the pros, however (but still only three years after high school graduation, so they usually get at least a few years of college education).
Currently, 46% of NFL players have college degrees, but the NFL encourages those without degrees to continue their studies while in the NFL in the Player Development Program (started in 1991) to prepare them for life after their NFL careers are over, so many of them do go on to get degrees while playing in the pros. However, most college-level players who choose to go into coaching regardless of skin color prepare for that while at university and thus continue on to achieve their degrees. It's a very different career path for most NFL coaches (who often have mediocre playing careers) from that of players. Whether you go into coaching or playing the opportunities, expectations, and resources exist to finish high school and get some college education and possibly a degree both before or during your pro career.
But, again, I think you've misunderstood Mr. B. He doesn't say that there is no racial problem. He says that the problem isn't that there have been - and are - few "black" coaches, but that prejudice is affecting hiring decisions - it is the reason that we see and have seen so few.
Affirmative Action or the Rooney Rule in and of themselves can't force people to change their minds and stop racism; nor were they intended to (however it can sometimes have a positive effect on racism by forcing bigots to work alongside the people they looked down on or isolated themselves from). They were meant solely to address inequities in hiring practices that occur as a result of racism, not racism itself.
No one is being given preferential treatment with the Rooney Rule. They are not required to hire minority coaches, only interview them. If they wanted to, the percentage of coaches could remain at 6% today. The fact that it is at 22% shows that once they are given an opportunity to at least get a foot in the door black and other minority coaches are just as qualified and have just as much a chance at success as white coaches do.
Ideally, a hiring system intended to fight racism would be indifferent to physical prejudices. Perhaps the identities and physical appearances of the candidates might be masked somehow. The Air Force has ceased using promotion photos to avoid unfair advancement of more attractive persons; modern technology offers some possibilities for other appearance-blind promotion systems.
Are we to care whether someone has unattached earlobes or attached earlobes merely because some persons think that the kind of earlobes defines the kind of person? All concepts of race are no less ridiculous.
No one is arguing that judging people solely on their race is a logical decision. They're arguing that unfortunately there are still a lot of people who judge others for such illogical reasons as the color of their skin and until such time that that becomes an insignificant issue in hiring practices safeguards should remain in place to ensure at least something closer to a more even playing field (and it's unfortunately still not even close).
As far as earlobes and shortness and other such comments, it's more than a bit ridiculous to try and compare that to how some people regard even arbitrary factors like race. It really looks silly to continue bringing them up as a comparison.
But well-designed systems can be - and have been - developed to combat physical prejudice without adopting it. The Air Force no longer uses photographs when considering promotions, some employers mask names from applicant files (because certain names are associated with certain racial identities), the Department of Homeland Security hires personnel through an online hiring process that is indifferent to concepts of race - there are many options that can go far toward inhibiting the effects of physical prejudice.
That doesn't work in a high-profile situation like being an NFL coach because by the nature of the job you are trading on your prior record, experience, and to a lesser degree name recognition; and your prior records/experience are well-documented and easy to link to a specific person whether they are at the college or professional level.