This is true. Narrative stories are usually fictional, but some authors write narrative stories that are kind of similar to memoirs in the sense that they document a true experience from the author's life.
Narrative writing is defined by its plot, characters, and storyline. Basically, anything that tells a story and follows the basic outline of a story (exposition, rising action, climax, falling action, resolution) whether real or imaginary can be classified as narrative writing. So in conclusion, both personal writing/nonfiction writing and imaginary stories are considered narrative writing as long as they have a storyline.
