It's that little thing on the first page which starts out Fact! All secret societies, artwork, ancient documents well apart from that embarrassing mixup between the Dead Sea and Nag Hammedi scrolls that is blah blah are as described in the novel

The man can't even get well-known basic facts right; what are the chances he's right about anything else? The number of people who actually believe it's all true, without verifying any of it, is....scary.