The bomb that "almost" exploded descended on it's parachute. It did not hit the ground (or the water in this case) at terminal velocity.
Wikipedia:
"Three of the four arming mechanisms on one of the bombs activated, causing it to execute many of the steps needed to arm itself, such as charging the firing capacitors and, critically, deployment of a 100-foot-diameter (30 m) retard parachute. The parachute allowed that bomb to hit the ground with little damage."
So, to prove me wrong when I said your scenario of a nuclear armed missile detonating on impact was bullhockey you gave an an example of a nuclear weapon descending under its parachute... Are you about ready to give up yet?