I think the reality is that the word has two established meanings. One is the professional clinician meaning you describe here, and the other is the more popular meaning of "shy".
The bigger point is that when you try to communicate with people, if they're using the word as introvert(2), you're being a jerk if you're pretending they meant introvert(1), because that's the "correct" meaning.
The bigger point is that when you try to communicate with people, if they're using the word as introvert(2), you're being a jerk if you're pretending they meant introvert(1), because that's the "correct" meaning.