I look kinda lesbian, myself. I'm asexual, and while I've never had any platonic romance, I do lean toward females, though only slightly. I'm more likely to find a female asthetically pleasing, but more likely to find a male interesting to talk to. So who knows? It would really depend on the individual. I don't really know to what extent I set off people's gaydar. I should ask someone sometime.
I wonder if the "straight Aspie guys looking gay" phenomenon is due to the general tendencie of autistics to look younger than we are. I think I heard somewhere that when trans guys transition, they look younger because of their still-feminine features... So maybe a guy who looks younger, also looks more female-ish?
I can see why it would be a bad thing for people to think you're gay when you're actually straight. It could mean that somebody who would ask you out, doesn't, because they think you're not into girls. That would be pretty annoying.