It refers to Zanzibar as a "graphical" system, which I think was the first thing that snagged me on this. Your post does too; I assume this is a language snag? "Graphical" doesn't connote "graph-based" in American idiom, but rather "visual".
I don't think your writeup really captures OPA vs. Zanzibar especially well either, for the reasons given by the SpiceDB person upthread. It just sort of defines away the problem Zanzibar is trying to solve, while claiming that Zanzibar-type systems aren't deployable at the edge --- which is pretty clearly not true?