Why does this guy just stare at me when I make small talk?

Hi so I have a class with this guy and I try to remain polite and friendly with everyone and I try to make small talk with people just to keep things friendly. I don't hang out with any of them outside of class or anything like that. I just mainly keep the interaction between us at school. There is a guy who comes into class and he speaks to me and says "hey how are you" I always respond back and says I'm doing good and then I began to just have some random small talk about stuff related to class or other relateable topics that is related to the career field we all are either working in or hoping to work in. When I start talking about something briefly I notice that the guy just sits there and stares at me and doesn't respond. I feel as though at that point I am just carrying on and talking to myself it seems like. Why do guys just stare at a female and not respond when she's trying to have just a friendly conversation or small talk with them?

Why does this guy just stare at me when I make small talk?
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