That is correct, and an even better fictional example is the good short story titled I don't know, Timmy, being God is a big responsibility. But this is not exactly what I meant here. I don't propose any non-hierarchical or infinite simulation hypothesis. Rather, all I am saying is that it is not a logical impossibility that two Universes have such a weird yin-yang simulated-simulant relationship. (Even in perfect isolation, just the two of them, without invoking an infinite chain of universes.) Obviously it is acausal, but that is a probabilistic, thermodynamic kind of improbable rather than logical impossible.

Maybe an easier such example is a spatially centrally symmetric Universe, where you can meet your exact clone who always does what you do. Or my very favorite, the temporally symmetric Universe, a version of the Gold Universe. Or a Hinduist Universe where time goes in circles. The point is, the idea that we live in a constructed, causally almost-but-not-perfectly isolated part of the Universe seems just an aesthetically displeasing corner case when discussed in the context of all these imaginable interaction networks.