It isn't a hallucination because that isn't how the term is defined. The term "hallucination" refers, very specifically, to "plausible but false statements generated by language models."

At the end of the day, the goal is to train models that are able to differentiate between true and false statements, at least to a much better degree than they can now, and the linked article seems to have some very interesting suggestions about how to get them to do that.

Why use a word that you have to redefine the meaning of? The answer is to deceive.

your point is good and taken but i would amend slightly -- i dont think that "absolute truth" is itself a goal, but rather "how aware is it that it doesn't know something". this negative space is frustratingly hard to capture in the llm architecture (though almost certainly there are signs -- if you had direct access to the logits array, for example)