Well yes, I got my timeline mixed up, didn't I? Was trying to make the point that Garrosh being Warchief was still okay with Thrall, even after he killed Cairne. It's been awhile since I read that book but I swear I remember it being mentioned that Garrosh thought his blade looked strange, but he went along with it anyways. Magatha poisoning the blade was what paralyzed Cairne (and left him unable to defend himself), but Garrosh was still the one who made the killing blow.