I definitely think it is over diagnozed; and that people are being hypochondriac about it.
However I also think that the increase is real and not just due to either over diagnoze or better detection.
I agree that Hannah doesn't strike me as autistic. She may have a very mild form. Alternatively or combined with it, she may have been somewhat deceived by her managers and producers due to her relative lack of social experience coming from a rural, isolated community.