Why does he keep saying hi to me?

Anonymous
So this guy I have never talked to but I do have a class with him, one day he randomly said hi (my name). Then the next day I was presenting in class and he's like woohoo go (my name). Then today he said hi (my name) again. I'm not trying to sound superficial but why is he doing this even though we have never talked. I'll say hi but adding a name seems different? Also he only says hi to me when I'm alone.
Why does he keep saying hi to me?
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