you're the type to be going for milk and see someone you recognize in the dairy aisle, so you walk down the canned goods section instead and pretend to be looking for something else until the coast is clear, you may have an underlying issue that goes deeper than simple extroversion & introversion.
It doesn't necessarily have to go 'deeper' than extroversion and introversion. I used to be the same way: avoiding ppl i knew, avoiding their gaze, etc. i wouldn't even label it as social anxiety per se, it's more like you have a screwed up way of looking at the world.
tbh, i used to shy away from ppl because i assumed implicitly that they didn't like me. so i used to pre-emptively shoo them away because that was my way of saving face.
"oh, she's a 9 out of 10. hot girls tend to not like me, i'll treat her like crap": CORE-BELIEF: i don't deserve to talk to attractive women.
"oh he's a cool popular guy. him and his friends propbably laugh at me oon the low. i\ll tell him to buzz off" CORE-BELIEF: i'm ugly and alone and don't deserve to be with friends.
that's why i was never a popular guy growing up. i was insecure and projected my insecurites onto others, and this made me seem unfriendly. next time you see someone you know, take a risk and talk to them. 7 times out of 10 on my word, you'll end up having a pleasant conversation with them, that will leave you feeling good. not always, but most of the time. you should attack those negative core-beliefs that are adding an ominous tint to your view of the world.
that's why i don't advocate labels like introversion, etc because a lot of cats are just sick, and are looking for a way out, and the label and the arrogrance that comes with it is just a misguided way of them shoring up their insecurities.