I found a lot of the guys that do strongman are from a bodybuilding background...many powerlifters as well. Strongman incorporates explosive speed/strength with mental and physical stamina...nobody cares if your waste is small or how vascular you are...etc. There is also a lot of strategy involved in strongman competition.
Here's a few pics from the Beast of the East. I am an NAS LW amatuer and this was a very heavy contest for pros or amatuers.
575lbs truck axle dl for reps from non-standard height
Super Yoke 740lbs
Atlas stone for max height 330lbs (20 inch diameter)
Farmers walk 330lbs (each hand)
Keg Press for reps 225lbs