What is it about a man and winking? Is that flirting?

He works at a supermarket.
He just helps everyone there haha. I know I shouldn't think about it too much.

I'm just nice to whoever helps me, because it can be difficult there.

Whenever he helps me, and he is done with the task. He just winks at me and then smiles at me.
He does that every time I see him.

I also made a mistake because I haven't slept at all for few days. And yet he still winks at me and then smiles at me.

Why would he do that?
I just smile back because yeah why not? But I just get confused by him and winking at me.

I don't want to think too much of it but I do wanna know, is he just being nice?
What is it about a man and winking? Is that flirting?
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