Bush being wired has been speculated before, as a Google search will show. Then there was the Bushist request that no cameras be put behind the candidates. Faux News (wisely!) denied the request, which was not binding on them. Kerry's people might have tried to draw inferences, including as information older photographs showing objects, it seems, stuffed onto Bush's back.
What would you do, if you were Kerry? Tell Bush you know he's wired, and give him a pat on the back. He can't confess, and you'll have him rattled. He can't tell on you because he can't confess. If you are wrong, though, what then? I don't think Bush could tattle on you; that would raise the public's suspicions anyway, and claiming some paranoid lunacy is the sort of thing Ross Perot would do (even though in this case it would be neither paranoid nor lunacy, just the simple truth).