ChatGPT will do it too, it happily invented papers (with nice ideas! although it just merged two ideas most of the time) for me when I asked for it to write a literature review. Then again, we face the challenge of grounding correctly vs flexibility. My hypothesis is that the model was trained using feedback from non-domain experts as well, so unless we solve grounding fundamentally I would even go and say it is the expected behavior of the model. That is, it was probably rewarded to make facts that sound good even if incorrect, in comparison to facts that sound bad, which makes its hallucination trickier even if it happens less. No reason to think fine-tuning will solve it.