The photo makes it easy to have an opinion on what might of happened. If the vehicle was travelling at speed and the trailer disappeared into a bog it would really matter what was towing it. If you enlarge the second photo you can see sand heaped on the A-frame suggesting it nose dived.
It's a similar effect to hitting an object at speed. Rear vehicle (boat) suddenly stops. Towing vehicle keeps going. The photos don't tell the story. Merely the outcome.