I just came across this video and I don't believe this is improvised

https://www.youtube.com/watch?v=CcsSPzr7ays

I doubt very much that it was improvised. Such great talent I'm sure needed a lot of practice. Enjoyed from the first note to the very last. Such skill. Amazing! Nice find. Thanks for sharing

Fun to watch. Both artists looked as though they were enjoying the performance as much as the audience.