Figure 1: The Runt Rover set up for RC control.
The RC mode of the RoboClaw is used to take input from an RC receiver which in turn allows the RoboClaw to control all four motors. The robot shown in the video uses skid steering, also know as differential steering, where it operates similar to a tank. The combination of the RoboClaw and the RC transmitter and receiver make it easy to turn any robot kit in to a remote controlled robot.
See the following Application Note for details on setting up a robot for RC operation: RoboClaw RC Controlled Differential Drive Setup
For a written description of the project check out this Instructables writeup.