The key IMO is that it's easier to tell when a human is doing it than when ChatGPT is doing it.
If its training data includes rants by flat-earthers, then it may "know" that the earth is flat (in addition to "knowing" that it is round).
ChatGPT does not have a single, consistent model of the world. It has a bulk of training data that may be ample in one area, deficient in another, and strongly self-contradictory in a third.
Even in humans, this "pretending to know" type of bullshit - however irritating and trust destroying - is motivated to a large extent by an underlying insecurity about appearing unknowledgeable. Unless the bullshitter is also some kind of sociopath - that insecurity is at least genuinely felt. Being aware of that is what can allow us to feel empathy for people bullshitting even when we know they are doing it (like the salespeople from the play Glengarry Glen Ross).
Can we really say that ChatGPT is motivated by anything like that sort of insecurity? I don't think so. It's just compelled to fill in bytes, with extremely erroneous information if needed (try asking it for driving directions). If we are going to draw analogies to human behavior (a dubious thing, but oh well), its traits seem more sociopathic to me.
We both know what you meant though
I'm going to get pedantic for a second and say that people are not ALWAYS confidently wrong about things they have no clue about. Perhaps they are OFTEN confidently wrong, but not ALWAYS.
And you know, I could be wrong here, but in my experience it's totally normal for people to say "I don't know" or to make it clear when they are guessing about something. And we as humans have heuristics that we can use to gauge when other humans are guessing or are confidently wrong.
The problem is ChatGPT very very rarely transmits any level of confidence other than "extremely confident" which makes it much harder to gauge than when people are "confidently wrong."