...Okay so as someone who is both on the spectrum personally, and who knows at least two transgender people on the spectrum, if anything autism should strengthen the case for transition, not weaken it. Like, if their argument is anything other than autistic people being 'weird' - of which the most generous would be that our difficulties with social norms might lead us to defy gender expectations - then I have to counter with the fact that discomfort with one's gender identity can exacerbate one's ASD, because of the lack of stability and/or consistent norms both for one's self to abide by and with which for society to treat them. One of those aforementioned friends has specifically cited how HRT has lessened some of her more notable behaviours, and just brought a general comfort to her life.
That said, I think they're just suggesting that autistic people are 'weird', which is bollocks.