What does it mean when a guy sighs?

I was walking down a hallway with my friend and my crush seemed to be walking down the same hallway towards us. He was with about 3-4 other friends but for some reason they were extremely quiet. I'm pretty sure he was looking at me but when he passed by he looked down and did this loud long sigh. It was still dead silent after that. What does this mean?
What does it mean when a guy sighs?
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