That was a rear tail rotor malfunction. I'm rather positive of that. Without the rear tail rotor, centrifugal force from the main rotor blades makes it impossible to fly. The whole chopper wants to spin in circles.
the pilot did do a pretty good job of stalling after dive, just enough to decrease airspeed for a "softer" landing...
No deaths and all in stable condition is a miracle for a helicopter crash like that in a urban city.