Why did he ignore me!?!?!?

hey i have one question for you guys. a while ago i met a guy who used to have a crush on me a few years ago. i didnt meet him since then. now when i met him he said hi very quickly but didn't seem interested in talking to me. we used to be friends back then...but now he ignored me! the weird thing is that he was hiding and secretely watched me when i played my badminton match. why did he do that? was he shy? would b geat if you could help me! :)