How do you know it was fear and not something else?
Have you personally run him in barrels or did his owners run him the last time? If it was his previous owners, they could have been reselling because he bucked at barrels.
Not all bucks are bad. Some bucks are because the horse is just excited and want to express their feelings, even with a rider on his back. He could have been excited and threw in a buck to show it.
And those who were seen dancing were thought to be insane by those who could not hear the music