His right foot is controlling the percussion sounds, the left foot is doing the bass line.  There was a post below clarifying the percussion parts:

"the percussions are included in the organ and are electromechanical, not electronic.
i'm Alessandro, constructor of this organ "

I believe he means that the pedal being used must make the noise by releasing air on a percussion instrument,  and is not a "manufactured sound" like you'd hear from a synthesizer.

I googled "pipe organs and percussion" and here's  an explanation and picture.

Theatre Organ Percussion
Private Residence, Levittown, PA
Photo: Paul Jacyk

In the early portion of the 20th century the theatre pipe organ was among the most sophisticated mechanical and electrical devices ever built. Mainly made out of materials such as wood, metal, leather, and water soluble glue, a pipe organ consists of a large air blower, ductwork and wind channels, thousands of moving parts, and miles of electrical wiring connecting the keyboards to electromagnets and valves under each pipe via a 1920's version of a "parallel computer" complete with a programmable memory.

The theatre pipe organ is an acoustic instrument which does not use any modern electronics or speakers. (Modern electronic switching systems are sometimes used to replace bulky relays).  Sound is produced by hundreds of air blown pipes specially designed to simulate the voices of various members of orchestral instrument families such as strings, woodwinds, and brass.  Real percussion instruments such as drums, cymbals, xylophones, marimbas and others are used.

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So THAT's why it really sounded like a percussion band! TOTALLY cool! My grandmother played the organ during the silent pictures in the late 20s and 30s. She had this story we heard my whole life! They had the movie there, Phantom of the Opera, with Lon Chaney. My Pa was there watching it, and he was 4 at the time. There was this one scene where they showed Lon Chaney Phantom's face, and the face got bigger and bigger and bigger. By the time it started getting really big, my Pa had jumped up into Grandma's lap while she was playing, and everyone in the threatre was laughing at him! They were in a tiny town, so they probably didn't have a cool organ like these. I played on a pipe organ at my Ma's old church a couple times, and the keys were really hard to play. But BOY was it fun! There's just nothing like the sound you get from those! I don't know WHAT I'd have done if I got to have a drum band playing with me, too! Cool info! Thanks for finding it for me! fee

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Posted by: CannaLily
Date posted: Mon Mar 24 6:27:23 2008
Message:
Fee, watch the tape again and pay attention to his feet while listening to the music.  The organ makes the sounds of a band.  My MIL has one of those organs and is pretty good!

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I couldn't keep my eyes OFF his feet! When I play, it is barely all I can do to make my two hands go together! Doing pedals with ONE foot is way beyond me! But these people that go all over the place with both feet just totally have me in awe!!! fee

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