I see this guy around school. He started saying hi to me, then we progressed to having little conversations and small talk. But now it's like whenever I see him, he acts like he's doing me a favor when he talks to me. I don't understand why he's acting like this when he's the one who started talking to me first! Why is he doing this? I'm really confused.
not enough information to make an adequate guess. could be sth changed, either with you or with him. could be mood. could be you're reading things wrong. could be nothing.
Maybe he got to know you a little bit from talking and actually thinks he's better than you. In which case, he's a dumbass.