Yeah, I was a shy child, even my earliest memory, first day of school, is of crying in the classroom. Then the teenage years, certainly high school, had some phobia around people, seems like mainly in school though I'm sure it was learned at home. I wouldn't ever eat lunch in the cafeteria, too many people, would've had to be social.
Don't recall having any label on this behavior back then. But it has remained throughout the years. I've noticed it in others at times too. It's not an obvious thing. People don't know about it most of the time. It's like you develop little strategies of avoidance. You'd have to be aware and attentive to see it in others. Not sure many young people have such awareness, but being older now I can look back and see it was there not only for me. But at the time your constant self-consciousness makes you too focused on yourself. Maybe others noticed more than I'm guessing.