Eh, I have it on good authority that the whistle wasn't by the LJ.
Think about this, though. If the whistle was ever-so early (related to the catch), what impact did it have on the overall down? Answer: Absolutely none. Even if we discount the possibility of the TV audio being slightly out of sync with the TV video, the ball was well on its way to the receiver, before the sound is heard on the TV broadcast. On the broadcast, the catch is made milliseconds after the sound is heard. Absolutely no players reacted to the whistle in time to have affected the outcome of the down. So, IW or not, staying with the TD was, in the minds of smarter people than me, the right thing to do.
Although not necessarily approved for/by replay, this is really no different than an IW after a Team B player recovers a fumble in the immediate continuing action. Allow the action up to the point of possession. In this case, that would result in a TD.