Cape is a slang term that refer to people with powers (parahumans), and was inherited from the universal costume symbol of superheroes and supervillains - the cape. It applies to most of the parahumans in north america and is applied to other parahumans outside it. Regardless of how closely those parahumans fit into the "suprehero" paradigm.
A small note of irony is that relatively few parahumans actually wear capes. A hold over perhaps from the adapted culture of the comic books.