Horse Patrol (The Witcher 3: Wild Hunt)

In Velen I met two mounted nilfs. Not far from the bridge to the lands of Novigrad, there is still a field with the corpses of soldiers. Near the nilfs, almost under the hooves of their horses, wild dogs roamed about. They did not aggro at each other. My Geralt was on horseback and killed three dogs. The Nilfs are aggrieved at Geralt. Apparently they were angry that they chopped the dogs without asking. There are two riders each level 54 and a red skull. (My Geralt is level 40, Blood and Wine has not started yet.) The horse battle has begun. The lifebar of the nilfs was decreasing as it should be. Then there were two death cries.
HOWEVER, both continued to ride, swing their swords and attack. Lifebars have disappeared from them. When Geralt hits, the slow is gone. I removed the sword for experiment. The damage from their blows to Geralt did not pass. I loaded the previous save, there were no more riders at this place, only dogs.
In general, is it possible to kill nilfs or guards? I have never tried it in the game. Or was it just another bug?