Why does he stare at me, but acts normal when we talk (no flirting, etc) ?


A few months ago I caught a guy at my job staring at me and I haven't really stopped catching him since. He only does it from far away or when he thinks I don't see him. After work he'll stand by his truck and watch me as I drive out of the parking lot. Very blatantly. I keep my eyes ahead, I've gotten really good at pretending I don't see. When I do purposely catch him he quickly looks away like he's embarassed. I asked a friend to pay attention and she agreed that he is staring & staring hard. So I know I wasn't going nuts.
It's very rare that a guy approaches me, sometimes I think I'm invisable to men in general.
So I just started saying hi to him to gauge a reaction and now we talk more often but mostly small talk.
He usually does some silly gesture or joke to try to make me laugh as he passes by my area, but it's more friendly than flirty.

One Friday towards the end of the day I had nothing to do so me & some other girls went around helping the guys in the shipping department. I went over to help him and we talked
It was the longest we've talked. He asked if i lived in town, how old I was, if I celebrated turning 21 the right way, etc.. He's one of the most friendliest people I've ever met and is well liked at work so it was easy. Our conversation was just completely normal, just the same way I see him talk & act with everyone else. No flirting, didn't even really seem shy. Which is why I don't get why he stares at me. It's just more confusing now.

I thought after getting to know me a little better he'd realize how boring I am, but the next Monday he was back to staring.
Basically he doesn't flirt or show any heightened interest, but he stares and studies me from far away, when I'm not looking.

This has happened to me before in high school & that went on for almost a year and I never got an answer then either.
It's really confusing to me.. why would a person stare but not like you, flirt or show interest?
Why does he stare at me, but acts normal when we talk (no flirting, etc) ?
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