It could be, but I suspect not. I suspect you are just a private person. Nice is very much overrated and not a particularly good adaptive skill in most situations. It leads to complex guesswork between people - that's what most psychiatrists and psychologists do anyway. One with meds, one with words.

If you give nothing away about your thought process and you don't follow predictable patterns of behaviour because you think about things before you act, then you will remain an enigma. If they know they get the truth from you, then it's a useful skill to have. Even therapists need someone to talk to - and they seem to dislike talking to other therapists.