Ah, so the original author did a piss poor job at establishing what constitutes an evil spirit, let alone did any semblance of world building which has seemingly caused this world to fill in the blanks and get messed up in the process.
Moral of the story to and authors out there; actually establish a proper setting for your stories, and flesh out the world. Don't make things so black and white, or else your plot wholes will get filled up with a bunch of messed up mumbo-jumbo when your story becomes its own world. lol