Linda From Maine wrote:
As long as we all agree that both are highly subjective, and until you know the photographer's intent, you can't begin to judge "incorrect" or "bad."
A high key image is often going to mean some degree of overexposure. A low key image is often going to mean some degree of underexposure. Neither is an error when the intent yields the desired result. A moonlit silhouette of a couple on a beach at night is going to appear many stops underexposed, except for the overexposed moon. Is that incorrect or bad? No, it's just what can be done, given the contrast range of the scene. The couple will like it for what it is, not for what it is not.