The boxed AI runs inside a universe that follow the laws of Turing computing.

Nature is the stuff around us. A simulation simulates nature. The one who runs the simulation isn't part of that nature. The simulator can exist without needing anything from the nature in with John lives.

If I'm reading Harry Potter, Harry Potter lives in a world where magic happens. I don't. Those two world are fundamentally different. The magic that happens in Harry Potter's world is causally independent from myself.