They are not the same thing, even if a lot of people try to use them both interchangeably.
The modern form of autism as a diagnosis is born in the 1930s, when behaviorism is a dominant force in psychology. Behaviorism seemed pretty useful back then: while you can break a steam engine down to its individual pieces and study them individually, the study of the human brain presents 'a few' more difficulties. In that context, studying a person's behavior and their reactions to different interactions and environments did beat all other alternatives. The problem is that it's still a pretty limited approach. Is this person breaking down because they're tired? Or because they're sick? Or do they want to draw attention, or did they have a tough day before coming here, or are trying to manipulate their way out of-? You cannot truly know from the lenses of behaviorism, because you cannot (or could not) study the mind's internal state. However, the people working in the field still needed to justify their own salaries, so if they managed to get any results, they could claim they were making progress. We've been carrying a lot baggage from this period, one of the most harmful of which would be ABA therapy.
While the contemporary criteria to diagnose autism has improved somewhat, we can still find the traces of behaviorism everywhere through the psychiatric profession. I was recently watching someone take an online test (which, naturally, should only be used as an exploratory tool, but still points out to criteria used by doctors contemporarily or a few years ago, if you want to be optimistic), and a lot of questions are fairly questionable:
- Others have told me that I have trouble managing my anger.
- I have a tendency to yell at people when I feel frustrated or stressed.
- I am often beset by feelings of sadness.
- I rarely experience happiness or joy.
All of these questions make perfect sense for a behaviorist: all of these traits form part of a list of observed signs of a disorder widely studied, so they should belong to the same category as all the others. There is a significant problem though: how can you discern between traits inherent to the person's natural tendencies, and natural responses to a hostile environment? It can get pretty difficult for someone who suffers systematic discrimination to live a fulfilling life, but that's no reason to claim that ethnic minorities who suffer from racism are naturally predisposed towards anger or depression.
It is a given in autistic communities that autism is inherent to a person's personality. The scientific community has some trouble to take the last jump to that conclusion, because even though research often finds strong evidence of genetic inheritability, it isn't possible to predict an autism diagnosis in its current form from genetics alone. I posit that that just isn't possible, because the criteria to diagnose autism is an unholy amalgam of traits inherent to the individual and social/environmental maladaptation, which is not the same thing that we here refer to when we speak of autism as a neurotype.