That's the point, I believe. To call something 'real', and yet say in principle it couldn't affect us causally, is to contradict yourself. If you're contained in a set of nodes that are causally linked, then that is your reality. Any other sets of nodes that can't contact you just don't matter. Even if there was, say, a causal structure beside our universe, of puppies and kittens running around, it wouldn't matter in the slightest, if in principle we could never interact with them. If we could deduce from the laws of physics that they had to exist, then we would be causally linked. The point I am (and perhaps Eliezer is) trying to emphasise is that our reality is everything that can, and does, affect us.