The people who behave in this manner do a disservice to everyone, including those who are actually autistic. A big contributor to the collective knee-jerk reaction of distrust and skepticism towards "autism" is due to these self-appointed diagnostic evangelists.
Almost without fail, after I share my BPD recovery story, strangers slide into my DMs to inform me I'm actually autistic.
They never keyboard diagnose me with anything else.
But they never tell me what criteria they're using to make this determination.
It's almost like they think autism is a catch-all diagnosis. Where they got that idea, I haven't the foggiest.