What you're describing seems like the introversion/extroversion distinction, which is probably different from, although possibly overlapping and somewhat correlated with, the autism spectrum/NT distinction.

Indeed, I have slightly higher AQ than him but nearly median extroversion, and my experience is the opposite of his.

How many people are introverts?

Isn't introversion/extroversion a continuum? If so, what would that question even mean? How many people are tall?