Nikos I am glad you are not an exercise physiologist or a doctor. Upper body strength has nothing to do with cardiac or aerobic fitness, in fact a case can be made that the reverse is true.
The guy just gives it his all every second on the floor period. He has the body of an athlete just more of a soccer type, lean long muscles which are often surprisingly strong = power from the speed they generate as much as the mass. Don't under-estimate his leg strength, few players can hand in the air as long as he can to do reverse dunks etc. at times.