Clitoon
I think everyone falls within ambivert, because you behave differently in different situations and with different people, I also think external stimulus can have a huge part to play.
If your self-esteem rises, then you'l be more confident thus will be more extroverted in situations.
I can agree that you act differently accordingly, but say you are introverted. You can be just as confident or social as anyone, but you desire not to. You have a preference to be alone or in smaller groups. If your self-esteem rises and that makes you more confident and to be extroverted, I think that just means they were shy, not introverted.