But what would it even mean for the "real" structure of the universe to be non-local then ("If it looks like a duck, swims like a duck, and quacks like a duck...")? What exists beyond the node connections for us to have to "declare them local" as opposed to them just "being local"? The sentence you quoted would still be true even in a high treewidth universe; there would be just "more localities" to consider, I suppose.
But what would it even mean for the "real" structure of the universe to be non-local then ("If it looks like a duck, swims like a duck, and quacks like a duck...")? What exists beyond the node connections for us to have to "declare them local" as opposed to them just "being local"? The sentence you quoted would still be true even in a high treewidth universe; there would be just "more localities" to consider, I suppose.