Autism affects the way one processes the world, in every facet of someone's life. Including their perception of gender. For a lot of autistic people, gender is as arbitrary as many social rules, like for example, how eye contact conveys that you're listening.

Because of this disconnect, between how an autistic person sees gender versus how important society implies that it is, a lot of people find comfort in describing their gender as intrinsically intertwined with their autism. The whole thing about how autistic people process the world in a different way also plays a role, autistic brains are just fundamentally wired differently. That different wiring can most certainly lead to a complicated relationship with gender. Just a different way of seeing the world, when the person is serious about it.