I don't know. I don't think that you'll be able to find out the intention of the person just by the word HI. I guess he just wants to make friends with the girl.
Hi, einajesor. If he is just passing by saying hi, then I think that he is just being nice and polite. If he says hi and comes up to the beautiful lad with a flirty look on his face, then he may be after a little more than just a simple friendship.
Just saying "hi" is just a way for someone to be polite and friendly. I say "hi" or "hello" to everyone that I happen to walk by or see. I'm just trying to be friendly and that's all.