They're referring to continents. So overall, SEAs are the most physically fittest in the world. Mongolia, although genetically a mix of Central/East Asian, is geographically categorised as an East Asian country. The combination of Japan, China, Korea and Mongolia means East Asia overall has lower rates of physical activity compared to SEA. I am assuming native East Asians are probably in the middle after the Wakandans. By nations alone, Mongolia has the most physically active people. As for Japan I think it's their clean eating and diet that makes them healthier than westoids. The average westoid works out and exercises a bit more than your average Japanese but they also eat shit processed garbage. And owning a car in Japan is not rare. Just like the other developed nations, they also have modern conveniences that makes them physically lazy.