Arthur really does just see all this super natural shit and never brings it up. He’ll overhear someone in camp say “I’ve heard rumors of people drinking blood!” and he’ll just not even comment. He’ll have fought a vampire with his bare hands and then not tell anyone. He witnessed a supposed werewolf/feral man and then never mentioned it. He drank from a witches cauldron and didn’t tell a soul. He saw an alien spaceship and thought to himself, “That’s neat. Guess it’ll die with me.”