I did not have time to post a gut reaction before you posted the detailed info. But, I thought the match was ok, for that demo. I did think the horse struggled a bit with the weight in as much as she could not get her feet up off the ground very fast when transfering from one front leg to the other. I think she was a bit stressed, and if the speed were upped, you'd see it more, I think.
I did not have any problem with the guy's way of riding. Being that tall on a small horse means it's harder , you have nothing under your leg below your knee, and your center of gravity is higher above the horse's.
A 5 foot 4 inch woman at 260 would have to be very fit , and not have all the weight centered in her belly or breasts (top heavy).