Guy's Behavior

Why my professor doesn't make eye contact with me ONLY in his class?

My professor knows me better than other students. I like him as a professor. During his class, he doesn't make eye contact with me, even I sit front, middle and backward. But office time or when I meet him at school except class, he is really kind, nice and look at me a lot. One day, after his class finished, he looked at my legs. But he didn't say any word, ofc. and the other time, he was kind of waiting me in outside the room. Then, we started to talk. It doesn't seems like he doesn't care or like me as a student. But I don't know why he doesn't make eye contact with me only in his class. I know he is single, no girlfriend. So my friends told me maybe he has crush on me. But I don't think so..
Why my professor doesn't make eye contact with me ONLY in his class?
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