I haven’t recently read the Book of Jonah, but from my last reading I get this: Jonah didn’t like those in the City of Nineveh. It has been suggested that Nineveh had pillaged and raped Jonah’s home town, and Jonah was glad that God had intended to bring justice to the City. With that mind, Jonah would have been somewhat miffed by God granting grace to the people of Nineveh following their sincere repentance. In the last chapter, Jonah is waiting to see if God would still judge the city, and God providing him with shelter. When his shelter is destroyed, Jonah is not gladdened by the mercy of God towards a great city, but is angry by the circumstances surrounding him. We are left to wonder if Jonah ever appreciated grace over justice.
I would conclude that like so many of the happenings of the Old Testament, they did happen, but they are Holy Scripture to teach us about the ways of God. I certainly do not believe it is a ‘parody’ or an embellished story.