I actually don't think that the high percentage of autistic people who are trans/nonbinary has anything to do with how autistic brains work, and I think insisting that it does is a dangerous path to go down.
Rather, I think it has a lot more to do with the fact that people who are already othered in some way are more likely to question aspects of themselves and their identities than people who aren't othered.
Autistic people, and really, all neurodivergent people, are already the Other. Whether diagnosed or not, autistic people already feel different and already wonder why they're different. You can say the same about any Othered demographic. A cishet, white, able-bodied person in the US is less likely to question deeply how they feel because being of the normative class, they just assume others feel the exact same way as them (even if it's not the case).
Think about how many seemingly cishet people say things that make us as non-cishet folks tilt our head a bit, when they say things like "everyone is a little bi, doesn't mean you're gay" or "everyone's felt like a different gender, doesn't mean you're trans", because obviously not everyone actually feels that way and maybe these people could benefit from a bit more introspection, but they never considered it because they assumed everyone felt that way because everything else about their identity- whiteness, abledness, income- is considered The Norm.
So, an autistic person who already has felt different and othered their whole life, who has already been constantly questioning themself, is more likely to also question their sexuality and/or gender identity because they don't really have anything to lose and are already questioning anyway. Meanwhile, a neurotypical person with the same unaddressed feelings about their gender and/or sexuality is more likely not to address those feelings because they either think they're unremarkable or because they fear the repercussions of suddenly Not Being The Norm.
It's not that autistic brains are more wired to not be cishet, it's that autistic people, by being the Other, are just going to be more open to questioning their identity because their identity is already in question by everyone around them.
