Not the same person, but my experience has been that it's not some unique thing to autistic people, it's basically just the same thing anyone would do in a different culture.
Just stuff like "urgh this is so boring and uncomfortable, but i can't just walk out.." or "i should make sure to smile now so they know i'm happy".

In the moment it doesn't feel like a huge deal most of the time, but when you do it constantly you end up spending so much mental energy on it that you get exhausted, at which point i need to immerse myself in stuff like sitting at the computer or going for a hike, where there's no need to mask and i can get the mental stimulation that i need.