If you watch the jump carefully you'll notice that he takes off (launches) from the prosthetic leg. I wouldn't be complaining too much if he took off from his real leg.
Look at the kangaroo, a kangaroo has a very long Achilles tendon. This allows them to be very efficient in jumping buy storing up so much energy when it stretches out like a rubber band enabling them to jump very far with very little effort. Humans on the other hand, have very short achilles tendons and therefore do not have this mechanical advantage.
When landing, the impact force and weight of the this guy is absorbed by active elastic stretch of the prosthetic. When he jumps, the weight is accelerated by a recoil force due to elastic recoil of the the prosthetic. This recoil force is much greater than that of what our our achilles tendon plus the active contraction of our calf muscle can do.
This guy has the equivilant of a 15inch long achilles tendon. As if you look at the video when he actually makes the jump, you'll see the prosthetic "foot" is bent 90 degrees from it's normal angle. The human achilles tendon is a) not 15in long and b) doesn't bend 90 degrees.
As a side note, I would assume there is no "fatigue" or decrease in "springiness" of the prosthetic between his first, second and third jumps. He could always show up to an event with a brand new prosthetic.