Wut shud i do bout this guyish thing?

The reason he is trying to give you a high five and do little talk is to get your attention. Hes most likely shy and hopes that it will start a conversation. Guys sometimes dont know how to approach a girl and know what to say. The reason he gave you a high five was because he was comfortable with you cause he sees you. Maybe he got the nerves to come up and give you a high five. Sooner or later he will start talking with you.