Quantum locking only occurs in the presence of a magnetic field. If the disc was removed from the track and let go away from the field it would fall like any classical object.

The "locking" that occurs is due to the fact that for small forces which would cause the super conductor to move perpendicular to the magnetic field lines, the generated current creates another magnetic field that interacts with the field on the track.

Incidentally, the same thing happens all the time even without the quantum effect. For example, if you move a magnet near a wire, it will cause a current to pass through the wire through a process called magnetic induction. Whenever there is a current, there is a corresponding magnetic field. Therefore a second magnetic field is also created which interacts with the first. Why don't you get levitation in this case? Because the wire has resistance, and so the current is limited, and therefore the generated magnetic field is weak.

The reason the disc is steaming in the gif is because it is super cooled with liquid nitrogen. Superconductors are only superconductive at very low temperatures (which is why we don't use them for various applications all the time). As this disc warms it will lose its ability to levitate in the magnetic field. However, in its superconductive state, a very slight perturbation through the magnetic field (only in the orthogonal direction) will very VERY quickly create current in the disc strong enough to generate a magnetic field that cancels out the perturbation.

There is a limit to how much counter active force can be produced, however. It can be easily overwhelmed. This is why the presenter can so easily move it with his hand. He will have felt some resistance when he did so, but just a little.