Our "universe" simultaneously is and is not a simulation because reality is relative to the seer. It's a fun thing to think about but pointless due to our limited understanding on what would make one universe 'real' and another a 'simulation', since really they're one and the same, just at different scales. It is interesting to think about though whether or not our universe has a parent universe which it exists inside of. And if so how deep that nesting goes. If our universe isn't contained inside something else, does that mean our universe simply is everything? No way to really know.