Is he realy an introvert?

My boyfriend describes himself as an introvert, and generally I'd agree (he's a homebody, really hard to get to go to parties, and generally speaking is the strong silent type). But here's the thing that confuses me, introverts are supposed to keep to themselves or just hang with a small group of people at parties but when the time comes he's quite literally the life of the party. Everybody loves to talk to him and you can't go five minutes without hearing his big booming laugh. I thought introverts were supposes to hate interacting with strangers yet at parties he always has a crowd around him, many of whom are stranger. I just can't believe he's an introvert, I mean for heavens sake last week he and a friend, in front of a crowd of people, spent like half and hour with a guitar singing drinking songs. For a few days after parties he is completely untouchable, like he won't even leave his house except to go to work and even refuses to see me sometimes.But having seen him at parties I just can't believe he's really and introvert. Is their such a thing as a shy extrovert or is he just and oddball?