You're probably right. Although, I'm not sure if that's entirely universal. My boyfriend is very sociable and yet he gets treated more or less the same as me often. I've been trying to be more social but I have a hard time trusting people (I usually get used or abused by people who pretend to be my friends in order for me to do their homework etc.) or being even remotely comfortable with discussing most things that involve my opinion. I wasn't safely able to have an opinion when I was younger and I have to trust someone quite a bit to feel like I can have an opinion. A lot of times I don't even develop an opinion (especially in politics) because there doesn't feel like much of a point. I can't handle people who disagree aggressively anyway.

So I'm sure I just seem aloof and unempathetic. I know everyone comments how quiet I am. I try to join conversations, get buried by everyone else talking over me so I just listen.

Another note on being/seeming unempathetic...I still struggle getting my emotional needs met and so I have trouble meeting other people's emotional needs. I can do better than I used to, but still...it's difficult. And you can't make friends unless you can meet other people's emotional needs and I can't do that for multiple people. I'm still going to end up needier than most people which creates imbalances in relationships (which happened in old friendships).