The frame section appears to have failed (ripped?) at the stress riser where that crossmember joins the rails (or maybe from where one of the bed mount brackets is attached), probably because the frame rail was loaded on the edge of the lift adapter right below that point. The frame rail flange has obviously buckled as well, so it was probably just a really bad place to load the frame rail in compression (reverse bending) instead of the tension. It's likely the normal case of chicked-or-egg; did the frame web rip first at the crossmember or bed bracket, causing the lower flange to buckle, or did the lower flange buckle and then cause the frame web to rip?
That's the interesting part, they likely just happened to find the worst spot to load the frame in bending at a single point.