Many modern activities will put someone in close proximity to lots of strangers. Airports, public transit, busy streets, college parties, even big grocery stores all have lots of strangers. A person who doesn't want to be surrounded by strangers is probably feeling an ancient survival instinct. Now, if that feeling prevents them from visiting family, living a happy life, or accomplishing their goals, it's a problem. But I don't think feeling uneasy in a location filled with strangers is inherently unhealthy.
Likewise introversion isn't a bad thing. Some people would just prefer to be alone, and that's okay. Maybe it's a muscle they could strengthen, but I've known enough introverted folks who constantly practice social skills but never increase their inbuilt number of "social hours". They love people, love entertaining and meeting people, but as soon as that number is hit they go off into their room and don't come out for a few days. I don't think this is an issue, they've got a fixed amount of social energy and that's that.