This is the same technique that the NSA and CIA uses for counter-espionage to find moles.
Of course, they could sue those playtesters for breach, but would never win-- because:
1. There is no proof that it was them who drove out to an internet cafe in some major US city and posted the information annonymously to a wiki. For all wotc knows it could be net-trolls lucky guess. All they have is the circumstantial evidence.
2. Even if they could prove that the group did it-- they could NEVER prove which member of the group did the posting. Since all but 1 member of the group is innocent, all would have to be let off the hook. Innocent before being proven guilty and all that...