The chain is to connect the pedals to the rear wheel as you might expect, assuming you want to be able to pedal.
I see the rivan thing has a toothed belt rather than chain.
I see the rivan thing has a toothed belt rather than chain.
Instead the pedals work as a throttle to set the speed of the motor and to charge the battery while you ride, reducing depletion speed. It also harvests energy when braking.
If the battery in this bike dies completely, or is removed, you cannot pedal to move it at all. The "toothed belt" (gates drive) connects to the motor, with no link to the pedals.
In theory this design could have been done with no chain/gates drive using hub motors and still work much the same, given all the pedals are really doing is turning a dynamo-contraption to charge a battery.