Yes, the truth was that the StG 44 wasn't for assault, it was for trying to slow down the relentless onslaught of the Soviet infantry who kept overrunning German lines. Hitler wasn't going to call it the "We are f*cked gewehr."
Also, that book is about real assault rifles, which civilians can't possess without getting an FFL that would essentially make them an arms dealer. That's why it says "military and law enforcement" on the cover. One of my caving buddies once tried to turn his AR-15 into an assault rifle, and the ATF paid him a visit and seized every gun he possessed, which was a lot.