What a trip... I also built a Guitar Hero "bot" some 13 years ago.

Mine was not mechanical like this. Instead I spliced into the guitar with a microcontroller that I controlled via serial port from my laptop. I wrote software that analyzed recordings of the note chart, saved them to a file, and could play them back over the serial port by telling my microcontroller program what buttons to press.

I don't have any pictures of the thing any more, but some of the YouTube videos live on: https://www.youtube.com/watch?v=n1YE8Wwo2rs