It's just like playing a style back on your keyboard and moving the master volume slider up and down in time with the music. It is kind of common to a new user of a volume pedal, especially on a full organ since most people tap with their right foot and that is where the volume pedal is located. On the other hand, this fellow certainly did have his tunes down, it was enjoyable to listen to other than the volume issue.

Back in the old rock B3 days, most guys just pushed the volume pedal all the way forward and left it there. Then you would control the volume straight from the drawbars. This also made the percussion cut through like crazy (think Green Eyed Lady).