First of all, the article says nothing about "younger people" or age or generation, that was something the OP added and I'm not sure why. If anything the example from the 1988 class shows that in the author's opinion the "unsophisticated" viewpoint is not
limited to any age or generation group. Most of the 1988 viewers (probably roughly my age, I'd add) would likely react the same way to Singing in the Rain
if they saw it today.
I agree with the author that refusing to engage an older film on its own terms is denying oneself some great experiences, and even that it's "unsophisticated," but it is very common. I have read posters on this board who've said that if a viewer has to take into account a movie's time and contemporary frame of reference to appreciate it, it's not a good movie. I disagree strongly, but so what? It's just opinions and I'm not going to change their minds.
And it takes some effort, too, to familiarize oneself with the issues and cultural climate of a movie's era. And for many people, that doesn't go along with entertainment. That's completely understandable.
I think the author raised his expectations of the audience based on what kind of screening it was, and was disappointed when some of them acted like most "mainstream" audiences would. I can see being surprised if someone had represented themselves as being "sophisticated" about movies, but turning up at an arthouse showing isn't really an indicator of anything like that. And making audible comments and jokes during a movie is just bad manners, but not really surprising, either.
I will say one thing, though, that's generational: I am glad I grew up when I did, before home video, judge shows, infomercials and so on. You saw old movies and shows on TV all the time, and there didn't seem to be an "accessibility barrier" around them. If you were staying up late or inside on a rainy day you could see a musical or a war film or a horror flick or a western or a romance or whatever, from ten to fifty years old. And if it was good you got caught up in it and didn't care about how old it was, because it was what was on. I had a lot of fun viewing experiences that way.