I dont understand. You are bitching about this guy that didnt do anything wrong?
Basically anyway. He bolted the sliders to the body (correct). and he welded them, i'm assuming struts, to the frame (also correct). I guess he could have welded a tab to the frame and bolted the slider to it, but the slider should be attached to the frame for rigidity.
If you just bolt it to the body, and slide it on a rock, its going to cave in the body, and if you just hook it to the frame and not the body, the first rock will bend it up into the body. True sliders have to be mounted to both the body and the frame to withstand what they are intended to do.
So dont Dis this guy, if he didnt do it exactly the way you had it planned or invisioned. I dont think he did anything wrong.