Interactions with weird coworker

I (22F) have part-time job at popular fast-food chain as crew member. I'm working there since May. I have working at diffrent restaurant for almost year, so I have some expirence. I work often with John (name changed; M25) and our intereactions are just weird.

He ran away when I introduced myself and tried to shake his hand. He said his name and disappeared. He looked terrified. For the first few months he didn't respond to my greetings. Other co-workers told me not to worry about his behavior because he is very quiet and doesn't like people. I saw that he didn't talk much to other co-workers with a few exceptions. He attends work events. He tends to help other co-workers with carrying heavy things (he is quite strong) or with technical issues. I am no exception in this matter, but I feel reluctant in any form of interaction and he often responded to my statements with a 'Ha'. Regardless of what I have to say and whether it was supposed to be funny or not. When he took over my shift (he really helped me because it extended his shift by a good few hours; I wasn't even going to ask him about it because I knew he had a shift at another station) and I thanked him, he replied again: 'Ha!'

For his birthday, he brought home-made cookies. I've been hearing how great they are all day long. I finally decided I would go try them and told him so. He commented that I probably wouldn't want to eat them (I'm quite slim, and he... definitely isn't). I feel his eyes on me if I don't try to talk to him (I don't act like that on purpose).

I don't know if I'm over-analyzing this. I'm not good at social interactions (I've made a lot of progress over the last three years, but still i'm quite awkard) and I just don't understand what his problem is. I don't have similiar problems with others coworker.