Their conclusion was that zfs.ko, as a self-contained file system module, is not a derivative work of the Linux kernel but rather a derivative work of OpenZFS and OpenSolaris.
For example the GPL talks a lot about linking. Now how does that work with languages where there is no linking at build time (like Java)? The GPL's architects tells us that doesn't matter because its all in the same spirit. But that's just an opinion, you need a court to rule on that to be sure.