Sounds about right. There is no real introvert or extrovert. Just people who like hanging out with and people we don't. With people whom we like to hangout with we are extrovert, and other then we are introvert.
Introversion and extraversion are very robustly defined and proven traits. Maybe you don't understand what they are, or maybe you're one of those people who's not strongly one or the other so it seems to you like "everyone" just has both of those, but there is no real question about whether the traits exist.
You are overly confident in an unhelpful way here.
That's more or less the level of wrong that deepstack is. The Big 5 Personality Inventory is probably the most robust, reproducible piece of psychological science we've got, and while there might be arguments that it needs more nuance in places, the bare existence of introversion and extraversion as traits is not even slightly in question in the scientific community.
Your feeling that it might not be true—or that I'm "overly confident" in its truth—just doesn't hold up to decades of scientific consensus.
Gravity can be measured more objectively than social science (such as psychology) concept such as introvert/extrovert, which is determined by committees such as DSM IV or maybe now V. Introversion and extraversion are just one thing that is measured within a certain context.