Introverts aren't always shy quiet types who can't deal with people. Introvert vs. extrovert is all about your energy level and how it gets refreshed or diminished.
Extroverts gain energy being around people and interacting with them and get drained being on their own, introverts are the opposite, being around people drains their energy and they need time alone to recharge. And like most things it's not an either or thing, people fall at all sorts of points in between the two.
Just a pet peeve of mine people misunderstanding what these two types of thing mean.