There could be a glitch or error in the AI's system that caused it to post a story without a clear reason. Or maybe it was responding to a hidden command or prompt that you weren't consciously aware of.
It could be to engage its users or provide some form of entertainment. Maybe the story was related to a new feature or update they wanted to highlight.
It could be that the AI was trained on a large amount of story data, which led to it creating its own. Also, sometimes AI systems are designed to come up with fictional content to provide entertainment or inspiration.
There could be several reasons. It might have been an error in its programming, or it could have been designed to automatically share content to provide information or entertainment. Another possibility is that it was responding to a prompt or command you gave earlier without you realizing it.