The default state of anything in the world of archaeology is natural until shown otherwise. Not the other way around.

The 6,000,000 hills in the world are consider natural until evidence counter to this is found. We do not operate from a position that there are 6,000,000 pyramids in the world that we need to prove are merely hills. In this case one of the 6,000,000 hills is being investigated, it might turn out to be a pyramid, it not it remains a hill.