The rotor struck a cable, the Squirrel helicopter crashes

What happens in this video ?

Crash of a Squirrel helicopter in Auckland, New Zealand – The rotorcraft was erecting a seven story Christmas tree. The helicopters rotor struck a cable causing the aircraft to crash. Miraculously, the pilot suffered only minor injuries.
The accident happened in November 2011. The causes of the accident have been established: massive out of balance forces tore through the helicopter after it struck the lifting line, which was attached to the bottom of the helicopter and the top of a nearby tower. After raising the tower, the helicopter descended to hover at about 5m so the lifting line could be detached from its hook by the rigging supervisor on the ground. When the rigging supervisor jumped up to grab the line, it instantly tightened and touched the helicopter's main rotor blades. The force of the impact caused major structural damage and the aircraft hit the ground.