> the kids think [...] Most teachers
Random anecdotal claims from population A contradict random anecdotal claims from population B.
> I’m curious what the author has in terms of actual evidence here?
Well, it can't be any worse than you have, in that the paper you link to doesn't show anything about what causes that negative Flynn effect. It does speculate, and social media is not on even on the authors' list of guesses.
Did you have anything relevant?