Processing speeds in people with autism is typically slow. It can take a few moments to process what has been said to us, then we have to process the (hopefully) appropriate response, and then we respond to what was said to us.
Imagine you are at a party and you are introduced to someone. If you are neurotypical, you respond almost immediately. There is no pause.
However, if you’re on the spectrum like me, it may take around three seconds to respond. Coincidentally, the shorter-term/working memory slot is about three seconds in duration. That’s the time it takes to both process what was said and how I should respond. And in that time, I’ve probably been nudged by the person I’m with to respond to the greeting.
Of course, these long pauses are perceived as either uncomfortable pauses or, if you’re nudged, as your having ignored the greeting. Neither of which really help one appear “social.” It’s another way we are perceived as being socially awkward.