Yes, I always interpreted introvert vs extrovert as being about where we get our energy from.... introverts get energy from being alone, while extroverts get energy from being with people.
Aye ! Susain Cain describes the distinction quite well[0].
Introvert/Extrovert describes how social intelligence relates to energy increase and decrease. Introverts are more rapidly exhausted in using their social intelligence, whereas extroverts are more rapidly refreshed when deploying their social intelligence. The "way we feel" about social encounters is a symptom of (and thus a correlation with) the rise and fall of energy as we are part of the scene — where typically when we are losing energy, we're less inclined to view the situation positively (social anxiety then is engendered), largely do to our own lack of introspection and the effects of our poor participation/adjustment.
It's more costly for introverts to engage socially, and so the rewards (take aways) are strictly only harder to perceive.
I can enjoy myself at a party, whether I'm a wallflower or not, but after prolonged socializing I need to spend some time alone.
Please do not mistake introversion for social anxiety.