What was he doing? (I would ask Singles & Dating, but they're like 12)?

Guys don't just walk around a girl just to get noticed, it was just a coincidence. Since you obviously like this guy so much, don't waste anymore time and just tell him. If he's acting shy around you, he probably likes you too. Just go up to him, strike a conversation, and tell him how you feel and maybe ask him out on a date. Don't overthink it or overdo it because it will turn him away. Just be yourself, be confident, and things will work out. Good luck.