It's a tough, very dedicated sport/lifestyle. When I mean lifestyle, this is their lives. They live it, 24/7. I don't even think they strength train like we do with squats/deads/bench. AFAIK traditional sumo's don't lift. They eat like fucking horses, maybe out eat and train through their grappling methods, which are grueling.
Also this man's body composition is much different do to the fact that he's white, was a judo fighter starting out and wasn't living the sumo lifestyle as a teenager like these other gordos. Saw a documentary on it on ESPN once, was interesting.