How do you react to an avoidant type person?

I tend to feel sympathy for people who are quiet and not very social. If someone doesn't talk to me I usually assume that this person doesn't like me and I won't try to change that.
But when I find out that someone is like that to everyone I start to like that person.
I share my flat with 11 other students and I didn't yet meet all of them. But 1 girl told me there is a guy who always stays in his room and never uses the kitchen. She thought it was strange, but I thought it's such a pity I will probably never talk to him.
I use the kitchen sometimes and when someone schedules a dinner for all of us I join. But this is more because I don't want to be the strange German who is opting out and not because I really feel like it.

I think other avoidants would never suspect that I'm not a social person.

I think that i met only one avoidant person who didn't know she was avoidant and i only realise it now. She was my roomate at a dorm a few years ago, she only stayed in and learned, all the time, she avoided going out, talking to my friends etc. she talked to me but only about the studies, she was very concentrated on her studies. i talked back to her, but we never talked about anything very personal.

I always think that everyone else is much more confident than me, even if someone is quite shy, i can't see it and i am usually scared of people who appear too confident. I think that if i meet a person who seems to be avoidant, i will want to relate to them and get to know them better. just am not sure how to do that.