It was a Hail Mary pass, but for some reason the moronic Broncos decided not to cover deep. The safeties (both of whom should've been deep) were caught short.
It was 4th down and 9 with like a minute and a half left in the game. All they needed was a first down, they didn't need to throw deep so that's why the Broncos were covering short and the Jets caught them off guard by throwing deep which is why the play worked. That's a completely different situation to what the Dolphins were in and what is typically considered a Hail Mary play where your only option is to go deep. It was not a Hail Mary pass, it was just a long pass in the 4th quarter of a game to a receiver who was single covered.