That separation between internal preferences and external behaviour is already implicit in Dutch books. Decision theory is about external behaviour, not internal representations. It talks about what agents do, not how agents work inside. As parts of decision theory, a preference, to them, is about something the system does or does not do in a given situation. When they talk about someone preferring pizza without pineapple, it’s about that person paying money to not have pineapple on their pizza in some range of situations, not some definition related to computations about pineapples and pizzas in that person’s brain.
That separation between internal preferences and external behaviour is already implicit in Dutch books. Decision theory is about external behaviour, not internal representations. It talks about what agents do, not how agents work inside. As parts of decision theory, a preference, to them, is about something the system does or does not do in a given situation. When they talk about someone preferring pizza without pineapple, it’s about that person paying money to not have pineapple on their pizza in some range of situations, not some definition related to computations about pineapples and pizzas in that person’s brain.