Related: I saw a post today of a guy trying to work out how a bird projectile-pooped onto a glass door.
The bird did not projectile-poop, most likely a bird was trying to fly to whatever was reflected in the glass and hit the glass and pooped. This is common. In Chicago, you can walk around downtown and see poop on glass all over. It's all birds hitting windows. You don't see the birds bc some recover and fly, but A LOT are eaten (gulls/crows/rats) or swept away by maintenance workers.