How come there's a section Any% but not a 100% category?

Also what makes a run Any%?

Any% means "Beat the game" with no additional restrictions (aside from not using external tools such as game speedup, save states, turbo keys, cheat engines, etc. Basically anything you can do within the bounds of playing the game is fair game, you just have to beat it.

In this case, "beating the game" is all there is to it. There's nothing extra you can do in the run like collecting other items, secret endings, etc.

For other games that fit the case of 'any% = 100%', check out: https://www.speedrun.com/rayman_1 https://www.speedrun.com/kpl