The dirtiest horse I ever knew was one of the winningest. There was no in between with him. Either you were blue in every class or ate dirt. Just because he sometimes going around well doesn’t make what he pulled any less dirty. And it looked like it wasn’t the first time.
I think people are underestimating how hard it would have been to stick that. It wasn’t what he did on the landing side that got her off, that just finished the job. The horse left from a distance the rider neither expected nor asked for that was pretty funny, not only jumped way up in the air but really round at the same time, landed and stopped forward motion while having a round back with his head down. That’s DAMN hard to sit. That’s not a normal jump followed by playing, that’s a real tough jump.
Again, I don’t think the reaction was called for (or helpful, frankly) and obviously staying on and riding forward would have been better-- but I think a lot of people are way misjudging how hard that antic was to ride and how dirty that trick was. It seemed pretty clear to me that she felt it coming (and so this is not the first time) because otherwise he would have stopped and spun out and not jumped at all. That was not a “horse spooks unexpectedly” kind of thing. That really looked like a dirty trick to me.