I'm assuming he has good genes. Add lifelong grappling and (assuming) weight training for grappling to the mix and viola...you're built like a tree trunk.
Weight training for grappling consists primarily of the pulling exercises. Biceps, lats, back, and core training. I'm sure he works his lats, but he has some serious thickness throughout his back. I'm sure he does a variety of row exercises on top of dead lifts.