How exactly does that count as the disk lying? ZFS assumes that different block addresses with the same data point to different pieces of backing storage and t

How exactly does that count as the disk lying? ZFS assumes that different block addresses with the same data point to different pieces of backing storage and therefore have certain behavior in case of errors, but does the spec actually state that this is a valid assumption? Or is this just a case of ZFS relying on particular behavior from things that are implementation-defined or undefined?