I'm not an expert, either, but I've poked at this a little. From what I've seen, token logprobs are correlated enough with correctness of the answer to serve as a useful signal at scale, but it's a weak enough correlation that it probably isn't great for evaluating any single output.

My best guess is that somewhere close to the root of the problem is that language models still don't really distinguish syntagmatic and paradigmatic relationships. The examples in this article are a little bit forced in that respect because the alternatives it shows in the illustrations are all paradigmatic alternatives but roughly equivalent from a syntax perspective.

This might relate to why, within a given GPT model generation, the earlier versions with more parameters tend to be more prone to hallucination than the newer, smaller, more distilled ones. At least for the old non-context-aware language models (the last time I really spent any serious time digging deep into language models), it was definitely the case that models with more parameters would tend to latch onto syntagmatic information so firmly that it could kind of "overwhelm" the fidelity of representation of semantics. Kind of like a special case of overfitting just for language models.