Why is it being called a Rock here?

"The large variations on the light curves indicate that ʻOumuamua may be either a highly elongated object, comparable to or greater than the most elongated Solar System objects,  or an extremely flat object, a pancake or oblate sphereoid."

So its either a elongated oblate sphereoid or a Flat Pancake like Disc in shape.

Light curve observations say its mostly Metal right? A clump of metal, might be more fitting.