That just flings crap everywhere. There's no aim. The closest comparison in the real world would be something like a baseball bat. You can aim the ball if you hit it right. But, in an ulbernaut's case, there is no pitcher. They might have to dig up the rock (let me add they have no method of scooping, either) and then... fling it. I'm trying to picture how they could even get it off the ground. If the rock was larger than both claws combined, I could see an ulbernaut lifting a rock. But how would it be thrown? Ulbernauts do not have the dexterity to hold on to the rock through the movement of a throw. They could drop the rock on something, trapping it or smashing it. But there is no way they could throw a rock with aim.
There are also no rocks that an ulbernaut could feasibly move near anywhere they currently exist. So it just looks like they are casting BrW spells. I always thought they were wizards, which never made sense. And that's probably what the non-forumer noobs think as well. It seems like no one thought this through. Like, what were the developers imagining? Are ulbernauts supposed to be a crossbreed between manly bears and deadly chopsticks?