I think some people understand more when you say you’re shy as oppose to you saying social anxiety. Before I knew I had social anxiety I knew about shy people it’s a common term some people seem to grasp better.
It can be risky when you tell people because they can impose ignorance as oppose to understanding.
I just say "I've always been quiet." They don't actually care enough to press me further, it's just an observation they make.
Every time I answered with "I'm shy" people would respond with "No, you're not!" in a shocked tone, as if I had just confessed that I was a serial killer.