Be careful not to confuse an introvert for being shy. You can have shy extroverts too, people who do very well in social situations but aren't good with new people/things. Whereas typical introverts do very well one-on-one/small groups and in areas they have interests in.
Also, no, not all shy/introverted/quiet people are self-centered. It's just to which degree they get excited about certain subjects. I guarantee you if you were to approach this guy about something he really enjoys (hobbies, sports, area of study, himself) he'll probably perk up if he's just introverted.
If not then you might intimidate or otherwise make him uncomfortable for whatever reason.
Long story short, don't force him out of his bubble, he'll come out when he's ready.