When we deliver agricultural tractors on trucks in the UK, the tyres are pumped up hard, real hard, to stop the tractor bouncing loosely around on the bed of the truck.
The tyres on the m.v. seem to be very underinflated, and it's likely that on a bumpy take off this may cause snatch loading of the chains and straps by allowing the vehicle to move in all axes.
Agricultural tractors have (usually) no suspension system. Road going vehicles (almost) always have a suspension system. Military vehicles (usually) have highly compliant, long travel suspension systems to handle rough roads and terrain at (relatively) high speed. When these vehicles are loaded using either chains or straps, the chains/straps are preloaded to compress the suspension system. Properly preloaded, they cannot "bounce around". This applies to vehicles loaded into a military cargo aircraft.
In commercial cargo aircraft the floor panels cannot handle the high downward point loads created by vehicle tires and so the vehicles are first loaded onto pallets. The pallets then spread/direct the downward loads to the rollers and rails which distribute them to the seat tracks which in turn distribute the loads to the floor beams. Usually when heavy vehicless are loaded onto the pallets, dunnage is placed under the vehicle chassis and the tires are deflated. This is because the pallets also cannot handle the high downward point loads created by the tires. The dunnage effectively spreads the load over a much greater surface area of the pallet. Straps and netting then restrain the load on the pallet. All the upward, sideward, and fwd/aft loads are transferred to the pallet edges, which then transfers those loads to the pallet rails and locks. The pallet rails and locks are pre-engineered for these loads, so it's extremely wise to use them.
But in the case of a "floating load" (which this reportedly was) straps and netting transfer all the upward, sideward, and fwd/aft loads to various "D" rings installed in the rails and seat tracks. Thus most of the load engineering is tossed out and the loadmaster must do the load engineering "on the fly". Since each "D" ring is only rated to 5Klb, the loadmaster must be high knowledgable and extremely vigilant in how he ties down the load. Clearly, the loadmaster in this situation was in over his head and/or tragically negligent.
Physics doesn't care if the cause is ignorance or negligence, the outcome is the same. However, a court of law will likely care. We'll have to wait and see how the lawsuits associated with this tragedy turn out.