Could just mean smaller friend groups as well. I conceptualize the major difference as introverts recharge by being alone and extroverts recharge by being around people. There was some recent research that disputed the concept of introverts and extroverts altogether, noting that when introverts became more regularly connected to people, their mental health improved. Introversion might just be the sum of our fears about connection that keep us from living a fuller life, with avoidance taking the role of an unhealthy coping mechanism for being unwilling to face our social fears. I say THAT because a lot of research has come to the conclusion that we are wired for connection and that the presence of close relationships is a strong predictor of the length of our life.
I also say this as someone with raging social anxiety, it sucks and I just get overwhelmed within a couple hours.