We know they are, and the author of the article cites the proof. LLMs do hallucinate, there is no way to make them not do it, because of the way they work.
The popular answer is sometimes the wrong answer.
These are statistical systems, so guaranteeing any particular high level behavior is not possible because of that. But given that they're working with natural language, that was never going to happen anyways, for the obvious language theoretic reasons.
The more appreciable interpretation of the claim is that they can be nevertheless tuned so that this issue becomes practically resolved. Contending guarantees and theoreticals is simply misplaced, these are not formal symbolic reasoning systems being buggy.
I did. I used that phrase.
"not slop cuz pretty useful" = slop argument