There's no way I would describe you as introvert though, you were perfectly happy at the BBB chatting away to people you barely knew both years.
But that is learned behaviour.
Even the biggest extrovert could be completely socially inept, and on the same token, an introvert can learn very sophisticated social skills, if they choose to do so.
Part of the reason I can and do engage complete strangers in conversation is confidence and curiosity, and a concious effort to overcome my natural inclinations, of remaining aloof and distant. Letting those inclinations manifest themselves would be detrimental to me.
It's about ones inclination, not what one does. An extrovert thrives on human contact, and the more they get, the better they feel. If they were to lock themselves away for days on end, they would experience an amount of discomfort in some way, where as to me, long periods of solitude are essential to my wellbeing. I thrive on it.
A small crowd, I can deal with, for a while, but the hightend state of awareness that I require to function in that environment leaves me exhausted. I cannot understand how going into a crowded pub can relax people at the end of a week. That just makes me ill. I just withdraw.