If someone substituted all of your sensory inputs for something else for your entire life, how would you notice? If you wore contacts from birth that made the sky red and earbuds that censored when people said it was blue, on what basis would you realize that was wrong? I don't see what this says about the architecture of your brain, and I don't think it's the point being made in the paper. That the training data must statistically connect to reality in order for the model to model reality doesn't seem that important.