A lot of us were very new to meeting people at nineteen and how to take what people said - I think most people are, no matter how smart they act. That's the thing - others are figuring out all this at the same time you are. He may be too (or not).
Do you know his name? I'm thinking I'd say hi, Mike (or whatever, and smile) when I saw him again. Maybe ask how he is, because you may be wondering about that.
That's the thing I learned once I got an afterschool job, to get off of my interest in me (I had sort of a closed life as you describe yours but not with your difficulty) and listen to other people.