Admittedly, I was doing some guessing, based on many years of programming experience (but not BIAB type). I haven't looked at the video, so I can't speak to that. However, I still think the RT generation can be done w/o any MIDI related messages to an "engine". All the info needed is in the chord chart window. If you listen to the raw RT WMA files, I think you'll find each "set" plays over the same sequence of chord changes at a fixed BPM. Therefore, appropriate playing for any chord in the song key can be found to fit the chord chart.

I'm not saying I'm right, but I could be. Only PG Music knows for sure.