(Qov, 7/29/2013): [Okrand] appears to agree that this implies {Sor} means speak literally, and that this is connected to the expression {lugh: Sor rur} ["correct as a tree"]. The pun with sure appears from his reaction to be intentional.
We actually know what the pun is, and "sure" ain't it. But I won't say it, as I think people should try to figure it out on their own. (It is found on this mailing list if one wants to cheat.)