Hi Kvmum and welcome!
I thought I knew what being introverted was, but I didn't, and I'm embarrassed that it has taken me this long to work it out.:(
My son is definitely on the extreme end of things and I have struggled and worried over the years with what I saw as his "self imposed solitary confinement", lack of friends, lack of social life and so on. Then on the other hand he could stand up in front of the school and give a speech no problem, I just didn't think the two went together. Now it is finally (duh) making sense to me and maybe, just maybe I will start worrying a little less about him being lonely. Oh, and I will have to put this into practice:
Second, when you see an introvert lost in thought, don't say "What's the matter?" or "Are you all right?"
Third, don't say anything else, either.
If only I had a dollar for every time I have said those exact words.