The pilot appeared to approach the drop very low, quite fast, and possibly in a slightly decent.
Almost immediately after dropping the load, there was a dramatic pitch up, which appears to have been the cause of the failure. As others with engineering / aeronautical knowledge have said, dropping the load by itself doesn't instantaneously add any load to the wings, so it should be discounted as the direct or sole cause of the over-stressed wing. Most likely, in the adrenalin rush of the drop, the brain's messages to the hands on both the release control and on the joystick might well have become conflated to a significant extent. This might have been exacerbated by the rapidly approaching trees, and even the desire for a dramatic exit - after all, the desired effect was a dramatic display. Whether for not and pre-existing faults were present, clearly and sadly it all conspired to end this pilot's life shortly afterwards.
It is a sad fact that too many pilots, planes, helicopters and innocent bystanders have become victims of this understandable desire to give the most dramatic display at various weddings, fetes, or other gatherings of friends / family, and often to pilots who do not have the display flying skill, judgement or currency to pull of the attempted maneuvre successfully, or without putting themselves and other at considerable risk. The desire to impress is a very dangerous one, which has and will continue to cost too many lives.