Can a helicopter really fly with rotors going this slow?
It's an illusion that the blades appear to be going slowly. It's actually a well known effect called the wagon wheel effect.

Essentially the rotor is spinning at close to an even multiple of the camera's framerate divided by the number of rotors.

This means that between frames the blades have moved a full quarter rotation (or a multiple of that). Creating the illusion that the rotor is moving more slowly that it actually is.