The reason that the can moves backwards is the transition of potential energy to kinetic energy. In the case of the rollback can, kinetic energy is transformed into an easily observable example of elastic potential energy, which is then transformed back into kinetic energy.
The way this works is when I rolled the can forward, I gave the can kinetic energy. Gravity exerts a lot of force on the heavy battery, pulling it down and causing it to resist the twisting motion of the rubber band. As the can rolls forward, the stubborn, heavy battery doesn’t turn with it, so the rubber band gets all wound up.
This converts the can’s kinetic energy into potential energy, and once all the kinetic energy is used up, the rubber band can untwist, pushing against the battery and rolling the can back towards you. Potential energy turns back into kinetic energy!