The difference is in where the torque is generated. In a traditional helicopter, the engines (mounted to the main body) generate torque to spin the main rotor. Since the body spins the rotor, by Newton's third law, the body and the rotor spin in opposite directions. Therefore, you need a tail rotor to counteract that.

With this design, the torque to spin the rotor is generated on the rotor itself, so there is no torque effect on the airframe. Note that there is still a (rotorless) tail with fins, probably to stabilize the aircraft in forward flight.

For more on this design, see https://en.wikipedia.org/wiki/Tip_jet

A typical helicopter has a motor between the body and the blades. Imagine using a screw gun. When you go to tighten a screw, equal force is imparted back on your hand because it's using your hand to push against.

These designs have the rocket motors pushing between the blades and air. This means that the spinning main rotor is just sitting on a bearing and the rotor is not being pushed off of the main frame.

However. You still need tail control to point it the way you want and to counteract inefficiencies in the main rotor bearing, that is why their prototypes have a tail rotor. That said, it's not As needed. If you lose the tail on a normal single blade heli, you are in for one hell of a ride. On this, a little forward movement and the vertical tail of the heli is likely enough to keep it straight.

In a normal helicopter, the helicopter is exerting a force on the rotors and thus feels an equal and opposite force that needs to be countered, either by a tail rotor or a counter-rotating rotor. This helicopter doesn't do that. If anything I'd think it might need a tail rotor to stop it from spinning in the same direction as the rotor, but I guess friction between the helicopter body and the rotor is low enough that this isn't a serious concern.

(The linked youtube video shows a version of this helicopter that does have such a tail rotor, though positioned closer to the helicopter than it might normally be.)

When the engine on top of a helicopter spins the blades, they exert an equal torque force back on the body of the helicopter. In order to just spin the blades and keep the body straight, you have to cancel that torque by using a tail rotor which creates a force way back on the tail that with the length of the tail, cancels it out.

In the case of this helicopter, the force to spin the blades comes from the tips of the blades, expelling gas out the tips will push the blade tips forward, so the body doesn't push on the rotor blades at all to spin them.

It is, the tail rotor is needed because on a conventional helicopter the main rotor is spun using a torque force from the helicopter body, through the engine/gearbox, and into the rotor. On this helicopter, the force is from the rotor through the rockets to the air, there's only a tiny friction force dragging the body along with the main rotor, and it looks like that's small enough to be counteracted by the aerodynamics.

Because the rotation is caused by a force at the rotor tips, so there is no torque on the aircraft. A conventional helicopter has an engine that is rotating a shaft connected to the rotor, so the engine is creating a torque on the shaft which causes the rotor to spin and then the shaft is creating an equal and opposite torque on the engine that is causing the aircraft to rotate the opposite way, which the tail rotor cancels.

The equal and opposite torque is provided by the blade tip rockets instead by the helicopter body.