What does it mean when a guy is looking at you and turns away?

So there's this guy who I barley talk to who sits across from me in music .today I coincidentaly looked at him and he was looking at me, and we looked at eachother for a splitsecond and he looked away. This happened 2 timmes already. And then after school I was standing outside waiting for someone,I look up and there's this guy I barley knbow looking at me, and I look at him, and he smiles and still looks, so I turn away. What does this mean? Help?What does it mean when a guy is looking at you and turns away?
It either means your ugly and doesnt want to look at you or (the more reasonable answer) he thinks your pretty and out of his league and really wants to get to know you (hence the smile), careful how you play this cause if you arent friendly and smile back he might think your trying to give him signals of leave me the hell alone you creep. If you do think hes cute and you could maybe see yourself with him then be friendly back and careful on what you do or react to what he does.