I think society sort of frames introversion as a negative, as if we should all strive to be more extroverted. Introversion and extroversion, and the entire spectrum in between, is simply a way of framing how one gets mental energy. More extroverted people are generally energized by the world around them and introverted people gain mental energy from more alone time or in smaller group interactions. One is not preferable over the other, it is simply a theory of how we operate. Introversion is often confused with shyness and extroversion with confidence, but neither of those stereotypes are accurate. While each has some behavioral manifestations, the introversion/extroversion continuum is not synonymous with social aptitude.
I'd say I'm an ambivert and always have been. I often get every energized by being in big groups. I equally crave time to be alone and reflect. When I was drinking, I often behaved erratically. My behavior made me appear to be extremely extroverted (I would do or say anything-no filter) or extremely introverted (I didn't want to do anything that messed with my drinking time), but those were just behavioral states that were altered by addiction.
Alcohol can't make a person introverted or extroverted per se. It can make you behave in ways that aren't true to your nature though for sure.