However, humans do have some known failure cases that help us detect that. For instance, pressing the human on a couple of details will generally show up all but the very best bullshit artists; there is a limit to how fast humans can make crap up. Some of us are decent at the con-game aspects but it isn't too hard to poke through this limit on how fast they can make stuff up.
Computers can confabulate at full speed for gigabytes at a time.
Personally, I consider any GPT or GPT-like technology unsuitable for any application in which truth is important. Full stop. The technology fundamentally, in its foundation, does not have any concept of truth, and there is no obvious way to add one, either after the fact or in its foundation. (Not saying there isn't one, period, but it certainly isn't the sort of thing you can just throw a couple of interns at and get a good start on.)
"The statistically-most likely conclusion of this sentence" isn't even a poor approximation of truth... it's just plain unrelated. That is not what truth is. At least not with any currently even remotely feasible definition of "statistically most likely" converted into math sufficient to be implementable.
And I don't even mean "truth" from a metaphysical point of view; I mean it in a more engineering sense. I wouldn't set one of these up to do my customer support either. AI Dungeon is about the epitome of the technology, in my opinion, and generalized entertainment from playing with a good text mangler. It really isn't good for much else.