While the CDDL and GPLv2 are both "copyleft" licenses, they have different scope. The CDDL applies to all files under the CDDL, while the GPLv2 applies to derivative works.
The CDDL cannot apply to the Linux kernel because zfs.ko is a self-contained file system module -- the kernel itself is quite obviously not a derivative work of this new file system.
And zfs.ko, as a self-contained file system module, is clearly not a derivative work of the Linux kernel but rather quite obviously a derivative work of OpenZFS and OpenSolaris. Equivalent exceptions have existed for many years, for various other stand alone, self-contained, non-GPL kernel modules.
至於這種說法是不是成立，至少在還沒上法院認證前也還不知道... 不過看起來 Canonical 是頗有自信，打算將 ZFS 弄進 Ubuntu，上面有不少好用的東西...