I can't answer for the GP, but my basic argument would be that you can probably expect any universe to produce multiple civilizations capable of creating universe simulators. As such the number of simulated universes will be a multiple of the number of universes, which means it's more likely that you find yourself in a simulation than in a real universe. It's worse than that of course because those simulated universes will end up simulating their own universes, and so on...