if someone I knew said they read a book, even a very obscure one, and then summarized it to me, I'd have great confidence that they would get such simple facts

if someone I knew said they read a book, even a very obscure one, and then summarized it to me, I'd have great confidence that they would get such simple facts as "who are the characters" and "what are the major plot points" correct. People, especially people you know, have reputations, based on history and experience that others have dealing with them. People can be known as liars, and anything they say is colored by such a reputation. Humans have language idioms for communicating about and dealing with such people too, phrases like "take anything that person says with a grain of salt". Look at how George Santos' history of lying about his own experience is being dealt with. ChatGPT can be (is?) the same, and it has a bad reputation for truth telling. And LLMs' reputation is not necessarily getting better in this regard. The problem is that many people attribute output that came from a machine to be of higher quality (on whatever axis) than output that came from a human, even a human they personally know and have experience dealing with. This is the same kind of prejudice as any other, or perhaps a more insidious prejudice.