Why did they do that?

I was going to the store, and there was this guy that looked around my age and kept staring at me. He wasn’t a bad looking guy, but I didn’t want to make it obvious that I noticed him, still he kept staring at me. While I was checking my things out, he went outside to go throw something away. When he got back in he did like a whistling sound, and wasn’t the kind of whistling that you sing to. Also yesterday I went to another store and I was looking at things and I heard whistling again at me. Why is it that I keep hearing that when I’m around somewhere?
Why did they do that?
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