Narrative hyperbole is when the narrator of a comic book says one thing while the action drawn on the pages clearly show something else. Sometimes, in the case of speech hyperbole, it is a character who says one thing, while the pages show differently. This does not mean the narrator or the character is always wrong. It only means that in the case of such conflict, the actual scenes overrule the narrator or character text.
An example of this would be the Ten-Eyed Man, who Batman and the narrator called "the most dangerous man alive", and who was actually a very lame and low-powered character.