I think social anxiety is paying too much attention to who/what is going on socially, around you. If you were to go to a party/class/meeting, etc. you would "avoid" certain situations, types of people, would look for and see different constellations (two girls around a guy, you wouldn't approach whereas three guys and a girl you might), some of which would be more/less favorable for you. It's a bit like having a phobia, you might pay attention to "elevators" too much if you're afraid to ride in them