Sure, of course it's all fiction. LLMs didn't exist as a concept when TNG was being written, so of course they didn't write them to do that. Data was also an AI, and the holodeck was able to create a Moriarty so intelligent that he became self-aware and avoided deletion.

My point is that modern LLMs are an approximation of intelligence that permit contemporary computers to respond to novel stimuli in a way that seems like intelligence. The computer on the show was far more advanced because it was fictional and set in the distant future. They never bothered to explain how it works, but there was nothing approximate about the intelligence it created in the holodeck.