Daniel pretty much made music wherever
he went with whatever was available. At home in West Virginia, he used
the family piano. In my garage in Texas where he wrote Yip / Jump music
he either brought with him or bought at a garage sale a small "dime
store" toy air-organ. That's the same "toy organ" that he made this song
with.
The pounding is him "slapping" the keys and
"chord buttons" and getting a noise out of the plastic case (which if I
remember was badly cracked). For him, I think that's just part of the
"noise making" which is "making music".
So - I agree - it is a "pure expression" -
making music to make music - not really knowing if anyone else would
appreciate it (but hoping they would!).
Your reaction to that song shows that you are
sharing in some ethereal human communication that is similarly
understood by many others. Interestingly, it crosses language barriers,
as Walking the Cow is still well loved Japan amongst the languages of
Europe and the Mediterranean..