Hey, thanks for replying to explain :)
I went and revisited the game after reading this and I guess I see the idea? The game can be beaten indefinitely by shooting the wall next to the player, not moving the mouse at all and just clicking every few seconds. The balls just bounce side-to-side and wipe out anything on the screen as they spawn in.
I did not notice the ammo counter because it is not visible when playing the game full-screen.