We really don’t understand the human brain well enough to have confidence that the mechanisms that cause people to respond with “I don’t know” are at all similar to the mechanisms which cause LLMs to give such responses. And there are quite a few prima facie reasons to think that they wouldn’t be the same.
The mechanics don't have to be similar, only analogous, in the morphology sense.
FWIW, I'm describing failure modes of a human, not mechanisms.
I also think "would" in the comment I'm replying to is closer to "could" than to "does".