There is quiet and there is can’t-have-a-normal-conversation with someone. When someone asks if someone is quiet, I would tend to think they were trying to ascertain if the person has a personality. I wouldn’t want my girls redt to “quiet” boys (they have been, and it was like pulling teeth to get the boys to talk), but I would not want them redt to loudmouths, either. The idea is for there to be a balance and a clear and pleasant.
Quiet does not necessarily mean introspective, nor does it mean deep and thoughtful. A person can be quiet because he or she simply has never learned how to interact with people. They could be overly shy. The kind of quiet that comes from being introspective, shows the personality in other ways, through strength of character,and also through intelligent conversation. But again, that is NOT what people are usually asking when they ask that question.