I couldn't find any information about it on the internet, and I'm not willing to go through Plato's work searching it.
Since just the title of an obscure story dosn't exactly give any context for the question, here's a copy of the story.
The story itself is fictional, yes. But it seems like it may have been inspired, however, by some passages in the works of Sokrates' followers where their characters equate "goodness" with "usefulness".
Examples: Plato, Kleitophon 409c; Xenophon, Memorabilia 3.8.5; cf. Plato, Republic 336c-d and the subsequent discussion. Note that the word used for "good", kalon, also means "beautiful", which leads to some mildly entertaining oxymorons (e.g. the question in Xenophon of whether a chamberpot is "beautiful").