Somebody should inflate a J-31 decoy on deck and watch the freak out that ensues.
... Uh, we've already seen J-35 mockup on CV-18 and it's probably at sea on or in the carrier.
It wouldn't cause much of a freakout because if it was seen on the deck on a satellite images, it would be seen as either a mockup or perhaps the real aircraft doing aviation trials on it which we expect in the near future anyway.
And if you mean the land based "J-31" why would that relate to Pakistan at all, given we won't expect the land based "J-31" to be on CV-18 to even get on the flight deck to begin with (it can't even land on it let alone take off from it), not to mention on a satellite image of this quality we wouldn't be able to reliably differentiate from a J-35 mockup versus a J-31 mockup.
All of which is to say.... This joke doesn't make any sense to me?