I'm sure you could use the actual drive chain (it looks like a cogged belt) to slow the vehicle down by removing energy from the rear wheel. My guess is that the front brake is only used for emergencies, and the bike works as a fixed-gear.
That's not an assumption. You can clearly see the brakes in the video which shows the intended use.
If it's single gear, you can simply stop pedaling to brake since it would be direct drive. In fact, that would probably be the easiest as I doubt this bike is capable of any serious speed.
