Why do guys turn around to stare?

I only see this guy occasionally and he used to mind his own business but after seeing me at a wedding, I noticed that he stepped out of where he was standing to stare and smile at me.
A couple of minutes later, he did the same as I was eating and didn't look away when caught. I then noticed that he was facing the other way, and after hearing someone talk, he casually glanced over to see who it was. When he noticed it was me, he completely turned around to face me, and just stood there staring and smiling at me, it was for like 10 secs or something, longer than usual, so I just walked out of there. He doesn't come and talk or anything.
Why do guys turn around to stare?
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