We mustn't forget that artificial intelligence is just that ... artificial. It puts things together based upon chance and probabilities. It's quite possible that the 'novella' is a complete or near-complete version of something on which it was trained.
Lots of software-oriented people, at least in older age groups, must have written one of those "report writers" that churn our pages of apparently intelligent verbiage, using all the buzz-phrases of the day, but actually saying nothing meaningful. Much like some humans actually
ChatGPT is clearly doing a much better job of beginning, middle and end, and wrapping up the story sensibly, but its still really an enhanced version of the same thing.