From my sources..... ........
APU was inop. Two outboard engines started at the gate. It was gate 159 that requires a nearly 180 degree turn during the pushback onto taxiway C. For some reason, it was decided to return to the gate by tow with the engines still running. While in the tight turn back toward the gate was when this happened. "Brake, Brake, Brake" was yelled to the pilot when control was lost but obviously, by the time brakes were applied the damage was done.
No doubt there is a lot of inertia if you are towing a heavy A380 in a tight turn and want to slow down. Some airlines do have a max number of engines to be running while being towed forward and/or a maximum speed. This could be an example of why.