I thought it was obvious (as in from the double-picture sections) he was pulling a Les Paul.
I remember criticism about Paul "faking" the music with tape recorders, but nowadays they just call it mixing.
One of the greatest examples of "mixing" is the famous "Good Vibrations" number by the Beach Boys. It was actually done with different musicians in like four different studios over something like a month. That little ditty has the structure and craftsmanship of a full-fledged symphony.
Incidentally, re the present clip, did anyone notice all the oddball gitboxes he had on the wall near the end?
Terry
REF:
https://youtu.be/uVlSVkzbJDA (4:19)