Either.. 1. They don't actually believe it, but its the narrative they want to give to the NPCs. Maybe they are paid to spread the narrative, maybe they have status to gain from doing so. Or 2. They are complete idiots who never had any education on American history. Both seem plausible. Its difficult for me personally to believe that these people could have possibly gone throughout their lives not understanding the founding of the nation, until I remember that they most likely never had a public school education. The education they received was likely carefully curated, and the people they associate with are obviously like minded.