Why did he look upset after this?

There's this boy that really likes me and pesters me to kiss him a lot. I've told him no everytime. Then yesterday he's like if my team wins, you have to kiss me. I told him fine. His team won, and after the game I walked up to him and gave him a really long kiss. He's asked if that was just because his team won, I nodded yes. Then he's like, "Oh I see" and he looked sad/upset and walked away.