They don’t say their child has autism (because nobody would believe them); they use the catch-all “autism spectrum” because it is so vague. NOBODY (including their closest friends) believes them.
Well, I can’t speak of this particular family. Who knows? They may be doing a munchausen by proxy thing. But in general, neighbors, friends, and family would be kinder to believe the dx simply because sometimes you have to be in the house to see the effects of the dx.