I know what this is. I once visited a psychotherapist, who has AS herself. She explained that those on the spectrum can experience emotions differently to NTs.
The way she explained it was by suggesting that a person's mood could be measured on a scale of 1-10. 1 indicates calm/ neutral, and 10 indicates full-blown meltdown/ extreme emotions.
When NTs react to different situations, their emotions can start at 1, and as they become upset, they may travel up to 2, then 3, then 4, and so on. They don't necessarily have to reach 10; they may simply be slightly annoyed, then return back to 1 when they've settled down.
Those on the spectrum can react differently to this. Now this is generally speaking of course, and it affects some, more than others. Some Aspies will sit on 1 for the majority of the time. This is what cause Aspies to appear "aloof". When Aspies do become upset though, Aspies can swing from 1 to 10 in a single move; missing all the steps in between. This is why Aspies appear to have "meltdowns".
Some Aspies may sometimes also mistake an NTs mild annoyance as a 10, but only because the Aspie may only understand the two extremes, and not the steps in between.