Lies are generally understood to have an element of deception. The enchantment (or whatever you'd call it) on pinocchio's nose has to do with morality, not fact. So, the first explanation, that he has to know he is telling a lie, seems to make the most sense. Unless the point is trying to be clever by inventing paradoxes in a Disney universe that is clearly not based on a 100% consistent model. In which case, if Pinocchio says that all the Disney worlds collide together in an epic explosion, creating a Big Bang which beings the Dreamworks universe.