What does it mean if guy waves his hand with no smile but staring at girl?

My crush is super shy. We haven’t had much chance talk with him yet but when we see each other, I try to be friendly (I am also shy) by waving hand with smile. He waves me back but no smile, staring at me.

Does it mean anything?

What does it mean if guy waves his hand with no smile but staring at girl?
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