Some of what you've quoted highlights my own belief on some of this:
Autism is also multiple things.
That may provide some insight about how there is not a "single `autism gene'" and how they hedged a bunch of these statements with "most" or "usually".
Maybe some day when we as a species understand brains better, some people will get a more precise label than "on the autism spectrum".
> Autism is also multiple things.
This rings true to me. As someone with an autistic loved one, I obviously think about it a lot.
If it were as simple as there being some simple genetic basis that gives you a single thing called autism, I would expect it, honestly, to have naturally died out long ago, just because it makes so many things harder for people that it cannot possibly have not had a disadvantage to reproduction.