Animation in general is more attractive to autistic people, exactly because smaller gestures/expressions are more obvious and expressive than real life. I'm personally obsessed with good quality/fluid animation in anime, so the expressions and over the top nature does nothing for me. I harbour some doubt that there are as many autistic trans people as people claim there are, though. Often they're socially awkward (but not pervasively so) self diagnosers who act 'autistic' (i.e. read about it and start applying that to their own behaviour) and say they are, but don't actually meet the criteria for it.

There are, on the other hand, many people who are on the spectrum and are gender non-conforming due to the lack of awareness/caring for gender expectations/presentation (I fall under this category), and as a result, many are convinced by peers, parents, psychologists or by online circles/forums that they're trans, and once an autistic person has a special (obsessive) interest in something, it's very difficult to change their mind. Becoming trans also allows them to feel like they belong somewhere, since the trans community is notorious for being inclusive and welcoming (so long as you don't desist).