Yes, they are auto-completers, but they are auto-completers that are layered AND operate in higher dimensional spaces. This throws all intuitions off, and I think makes it misleading to think of them as "just" auto-completers. That's part of the story, but not the whole of it.
I suspect we are much closer to auto-completers than most of us like to think, but we're also trained+incentivized by culture, education, parenting, socializing, to produce "useful" results.
Maybe part of the problem is in the data set: how much modeling of "how to admit ignorance or uncertainty" are in LLMs training data sets? If you read the internet, all you see is confident replies to other confident replies. Ignorance or non-confidence tends to elicit either a bluff or non-response. If you read technical literature, you see much of the same.
Maybe LLMs are trained on a dataset, and thereby inherit a culture that's accidentally biased toward ignorant confidence. In human conversation, if somebody asks a question and I don't know the answer, I say I don't know. On the internet, I just skip it and leave it for somebody else who thinks they know.
All this is to say: maybe a statistical autocompleter can admit ignorance instead of firing "neural noise" based on barely-there loose associations. Maybe it just needs a stronger pathway toward talking about not knowing when there's not a strong association.