Don't judge a book by it's cover they say.
Some of us only come alive in the company of others. When you meet someone that seems introverted in these group social situations, don't assume they are dull and boring.
We're all different and some people like to just sit back and let the extroverts take over the show. They just listen, observe and take it all in.
When you've all gone home and they're on their lonesome, they can really shine. Singing in the shower and dancing like no one is watching.
And to be fair, who's happier? The one that needs company of others to come alive or the one that parties around the house with a smile on their face?