Interesting post! First of all you should be glad you are getting diagnosed, I get the feeling not many in here have actually gotten a professional diagnose (me included). Secondly I think your psychiatrist may be right, it doesnt take that long to diagnose a person for social phobia (typical scared of social events, avoiding meeting friends family etc because of anxiety and being nervous), on the other hand, I think it takes longer do specifically diagnose a personality disorder. So hang in there and wait to see what the outcome is, but dont forget not to put too much stress into "diagnose", its just a way of explaining why you are like you are.

To answer your second question, I think social phobia is more of a thing that people avoid specific social situations because it makes them nervous/anxiuos. While they can be totally relaxed and social in other situations. It depends who they are with and the situations. And the anxiety comes as a result of irrational thinking, which can be treated and totally dissappear for that person to later have absolutely no problems with social situations.

AvPD on the other hand has more to do with each individuals personality, which hardly can be treated (maybe learn some tricks to get the focus away from the social situations). I think it's more of how you perceive reality, other people and yourself.
I am on this forum because I have been treated for social phobia many times, but havent gotten any better, its just sitting in me like never before! I avoid pretty much any social confrontation, and have been doing it pretty much my whole life, and also like Panda I take on this mask to try to be normal when I am around other people..its just not about anxiety. But again like i mentioned I have never been diagnosed with it, but my doctor agrees