I disagree, I think the anecdote of an adult over 30 years of age being diagnosed is a fair example of under-diagnosis. And since your comment was more on the over-diagnosis side, I think it’s fair to point out. That the visibility and lowered stigma contribute to the over-diagnosing. It can’t be helped. Medical professionals are subject to the same biases of visibility that the rest of us are, even if they should know better.

Also some patients are certainly self-diagnosing based on freely available information, be it valid or not, and sharing their diagnosis as if it was a real one. When others encounter these claims, their instinct typically isn’t to argue or accuse someone of being a fake autist so they update their own mental models with a “this is what autism looks like” and the trend continues.