As you can see in the video, the thieves took around 10 seconds for the them to boost the key’s signal into their transmitter, and then another 10 seconds or so to switch places and take off with the car.
Using the black box a.k.a. the signal amplifier, the guy pushes the signal from your car key to a nearby transmitter. Upon receiving the signal, the transmitter will then clone itself into another key of yours, fooling your car that your key is nearby and allowing the thieves access into your car.
While cases like this might be rare on our sunny island, it could still be good practice to put your car key in a metal box as it is said to be able to mask out the signal sent out by it.