Source of the mistake

"Kill!"  As the battlefield progressed from the phase of intense fighting to basically the cleanup, the morale returned to the otherwise beaten people of the camp. That's why, rather than just silently massacring every monster left on the plain, Layn decided to hold his horses back. 

The people that fought to defend the camp had to score a few more kills with their very own hands. 

This way of letting the soldiers vent the frustration caused by the losses and wounded was commonly unaccepted in modern times. Allowing one's troops to disperse and vent on the civilian population turned out to be a problem big enough to warrant a special council that ended with claiming this kind of action as a crime of war.