Couldn't smile at a guy, even though I wanted to?

This guy I didn't know at my university stared at me whenever he saw me. He would continue staring even after I'd see him staring. He would also deliberatley look into my car to look at me when I was sitting there. It was always a blank stare into my eyes. I was really unsure why he was staring, I'm pretty much a loner, so I thought maybe he thought I was weird. I looked for advice online and many people said it could mean he liked me, and that I should smile at him. So, the next time I saw him and we made eye contact I reeaally wanted to smile, but I couldn't bring myself to do it. I'm very shy and introverted, maybe that's why? I also don't know why he was staring in the first place, but I personally felt a weird connection whenever we made eye contact. Has anyone had a similar experience or just some ideas on why he was staring? Should I have smiled? How can I bring myself to the next time I'm in a situation like this? (Btw, I don't see this person anymore, so advice on talking to him specifically isn't necessary)
Couldn't smile at a guy, even though I wanted to?
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