A short story is a work of fiction that is usually written in prose and is shorter than a novel. Short stories typically focus on a single event or a small number of events, and they often have a single main character. Short stories can be any genre, including literary, historical, science fiction, fantasy, mystery, and horror.
In this case, the text is a short story because it is a work of fiction that is written in prose and is shorter than a novel. The text also focuses on a single event, the main character's journey to the underworld, and it has a single main character, the main character.