Pages with broken file links

wtf is this, and why are massive amounts of pages linked to this, without it appearing here. Even more strange, on the edit page, the category isn't visible, and I just made a page myself, and the category is there without me adding it...

EDIT: I think I found where it is coming from...
the "placeholder" file (link) If you go out of the editor you normally go to when clicking a red link (click the name of the file you are about the edit) you will see a list of pages using the placeholder file.
all of those pages have this category.