I would say that he is a good jumper because he is skinny (low weight) and has good leverage with his leg length.
Cat jumping ability (and therefore take off velocity - TOV) depends on relative limb length, relative extensor muscle mass (the size of the leg muscles), body mass (is the cat overweght - this has significant negative impact) and the percentage of fast-twitch muscle fibers (some cats and people have the kind of muscles that can retract very fast making he leg move fast and thereby increasing take off speed).
Often feral cats are much thinner and lighter than domestic cats because domestic cats are over feed and ferals underfeed.
Timmy, a stray cat that I feed from time to time, is a typical muscular stray cat with a massive jump. He can effortlessly jump up about 7 feet to the top of a wall when he goes home (wherever that is). He has long limbs, is of a perfect weight and very athletic.
My girl cat is old and overweight and I have to lift her up to the bed (she calls me to do it).
My three legged cat, Charlie, can jump up beautifully as he has long hind legs and a strong back but cannot jump down as he has lost his front right leg and the remaining leg cannot take the weight on landing. He wriggles half way down and drops sideways so that his rear legs hit the ground at the same time as his single front leg. He also likes to take up the meerkat positon. It comes naturally to him and he uses it frequently. This is unusual for a cat and it is due to his extra strong back muscles which in turn in due to he absent leg at the front! Here is the little fella: