800 lbs of meat from a 1200 pound steer? Note I said steer, not bull. And even then, most steers weigh about 1000, not 1200.
I call bullshit. Usually 50 percent of the weight of the animal is wastage, be it bone, skin, or entrails. I've slaughtered a couple and the most I've gotten from it is about 550-600 lbs or so. Even then, not all of that is usable, since there is still bone and fat that must be trimmed away.
An excellent (300 lbs) side of beef will yield no more than 200-225 lbs, and usually more like in the 180-200 range.
So for this guy to claim 800 lbs. of beef from a single 1200 lb. steer? Zero bongs.