Everyone in the whole world is the world champion of something. Could be something normal like running, or jumping, but it could also be something really niche like solving the Rubik’s cube with your tongue while being under water with your hands tied behind your back. You just need to find what you’re really good at and that might be your thing.
I think they meant it in the other direction: Every single person in the world is the world champion of something, not every activity has a world champion.