Why was he so happy?

I accidently bumped into this guy at the gym as I was walking out the door. I startled him a little bit but I just pretended to be on my phone to kinda avoid the awkwardness. Then as I stood outside the gym on the street, I turned around and saw the very same guy walk out. He stared at me, looking like he was really happy / laughing on the inside. I thought it was strange that this random guy was making eye contact with me while looking like he was laughing on the inside. He wasn't smiling at me but just looking happy on the inside. We just stared at each other for a moment and it got awkward so I looked away to prevent it from turning into a staring contest.

Did he think I bumped into him on purpose to get his attention? maybe he likes the attention? or is he interested in me?

Why was he so happy?
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