Too much fucking details. Introvert/extrovert is bullshit for me, everyone is unique and has it's own style and personality and IMO you can't label someone introvert/extrovert. At least not on that signs.
Someone likes to party, to have fun with people but at the same time when he gets a chance he likes to relax in a quiet place. What does that mean? Nothing strange, no introvert/extrovert bullshit.
Don't knock the theory down yet. Introversion/Extroversion is not bullshit; take a look at the theory of personality types, and then you'll have a better understanding of where all this introversion/extroversion stuff comes from. Like you, I used to think it's bullshit too because introversion/extroversion appears oversimplified.
Both introverts AND extroverts can enjoy partying, having fun with people, and having a bit of time to relax in a quiet place. What does it mean? Nothing significant.
An introvert focuses more on the inner world; the introvert is focused on the subjective. An extrovert focuses more on the outer world; the extrovert is focused on the objective. Introverts tend to feel drained after a long time in social situations, whereas extroverts tend to feel energized the more they socialize.
However, these things have absolutely nothing to do with liking to party, relaxing alone in a quiet place, or having fun with people. Both extroverts and introverts can enjoy both, but it would be the extrovert who prefers the parties/going out, whereas the introvert prefers solidarity and alone time.
Extroverts and introverts are both crucial for each other and for how societies work. Socionics is a russian psychology theory that builds off of Myers Briggs, Jung, and information metabolism, and it delves even deeper into how personality types interact with each other and how they are crucial for societies to function. For example, in the U.S. we have both a president and a vice president. However, if their ego functions conflict, they won't get along (see classic examples of Bush and Cheney, JFK and Lyndon Johnson) and society has a much more difficult time to function. If the leaders of the country can't get along, how will the society thrive? This is what socionics strives to understand and solve, and I think the Russians came up with it because the way their society functions is beyond fucked and really needs help in this area, so a demand for help in this area demanded a solution. Socionics is the future, but unfortunately it's only realized in Russia at the moment, and I don't see it being realized in the U.S. at any time soon.