The number I have frequently come across, which is the one Google seems to have picked up on, is that 70% of autistics are "something other than straight". In this study I cited here, it says that 41.2% of autistic subjects they interviewed were "sexual minority" which I understand as implying the same thing. Which means that roughly 3 out of 5 autistics are actually straight, not just that they're cisgender and allosexual, but in fact heterosexual. As for how much that varies from the general population, I couldn't say but 3 out of 5 is still most people in the group.
The reason I think this is significant is that issues that might be impacted by one's sexuality are a big concern in the autistic community, but sometimes there is an impression given that if one is straight, or even cisgendered gay or bisexual, then one is outside the mainstream and must be apologetic when talking about one's personal problems in this regard, which are in fact some of the very biggest problems faced by a great many autistics. Or in other words, cisgendered allosexual autistics who want to talk about these problems have their experience invalidated by the supposed "majority" for whom failure to find a romantic partner is a non-issue. That attitude seems supported by the 70% figure, but much less so if 3 out of 5 are actually straight.