IMO this ambivert thing exists because we don't have a good understanding of introversion vs extraversion. Extraversion is not liking to be around people, extraversion is stimuli from the outside world; you need a connection with what is happening outside of your head and it actually enhances the inner workings of your mind. I like going to the park and just ~feeling~, observing life happening (trees, birds, cars, people), while I think and think deeper on whatever is that I'm working on. I would not like someone to come and interrupt my quiet time with myself, but my quiet time with myself actually involves other things rather than only myself. It's what makes my thoughts keep happening and I love it.
An introvert, on the other hand, already has this stimuli coming from themselves, and that's why external stimuli can actually be tiring and overwhelming. Since I'm not an introvert, I don't know how to dissertate on it, but I imagine that an introvert's mind has its own power generator while an extrovert's needs energy from the world.
So now the question is: which one are you?