The fact that you’re saying “from the outside” is literally the point. Outside implies an inside implies dualism. Hence the thought experiment. If there was no outside the thought experiment inherently wouldn’t be.
Well, unless with dualism you just mean that there are two, you are simply mistaken. Just because my car has an inside and an outside, and I cannot determine the state of its gearbox from the outside w/o the car telling me, does not mean that this implies a ghost in the machine. Far from it.