It was not a gedanken experiment, though; it was a joke. The box is totally irrelevant, because a cat in a box is not in a box, because the cat is not isolated,

It was not a gedanken experiment, though; it was a joke. The box is totally irrelevant, because a cat in a box is not in a box, because the cat is not isolated, because the cat is actually a compound system already. If you had a single particle in a box, okay, yes, that's valid. The cat would not be alive and dead simultaneously regardless of the box because it's totally entangled with and decohered / observed by the other elements in the box. A single particle, or a coherent system, can be thought of as being isolated though. Do you see what I mean