Suspect this might be true. I was literally talking to H about this the other day, she called it the "brown boots effect" after I noticed one time her looking for a microsecond at my boots. "You don't like my boots" I said a bit later on. She said "yeh I do", and I pointed out I noticed her very slight shift in body language. She actually at that time remembered thinking "those are almost the same as his black ones, its strange how he has two pairs almost the same". Point is:
1. I noticed this minutia, literally, how the **** do you even notice someone doing that?
2. I attributed it to dislike in some way (confirmation bias).
It's absolutely insane the amount of stuff I notice, and then mistakenly attribute to weird stuff about me. Walking about, interacting with people, with this kind of mindset, where you have no way of finding out what people are actually thinking and correcting those distortions, its going to absolutely run wild, imo.
Yeah I often feel like my brain is on speed in general (though it's like a patchwork with some areas being deficient/slow and some too fast.) When I think about it it doesn't even just apply to social stuff. It's like I analyse a lot of stuff to the nth insane degree whether I apply a negative self bias to what I'm analysing or not (or whether it's even related to me.)
I think where the environmental factor come in is in where you apply that though. If you've gotten used to people reacting negatively to you then you'll apply that 'ability' to picking up on social cues that only apply to the people you learnt it from who treated you in negative ways and were likely over sensitive themselves.
Oh and the other thing I didn't mention in my previous posts which is another related thing I believe in people with SA is probably pain sensitivity. Someone can treat you like complete **** but you won't remember/care later if you don't have that. (In fact a small number of people don't experience pain, anxiety, trauma etc at all because they're on the opposite end.)