It looked to me as though the bottom of the rotor was masked. That means there are no retreating blades.And even if there were any, they'd be the same on both sides of the aircraft. It's the retreating blade stall problem that limits the top speed of helicopters.Also, the blades probably don't need to flap.
(When a helicopter is moving forwards, the rotor blade that's also going forwards has a much higher airspeed than the one "retreating". As they have to have the same lift, the retreating blade has to operate at a higher angle of attack. Thus the blade flaps from a low angle of attack to a high one and back again every rotation. When the airspeed of the helicopter becomes very high, the retreating blade develops such an angle of attack that it stalls. Gyroscopic forces then come into play. Rather than rolling to the side, the rotor disc pitches up violently and cuts off the tail of the helicopter!!)