Interesting. The horse riders took advantage of their mobility in order to bypass enemy lines and head straight to the headquarters, killing the marshal and other high-ranking officers without directly engaging with other forces. They'd then retreat quickly, leaving a few guerrilla fighters to continue taking advantage of the confusion and eliminate other officers along the way (in our case, the MC). All in all, their objective was to simply target the leaders, leaving the true strength of the army rather useless.
Our MC, predicting this, took advantage of this in order to properly retreat, suffering minimal losses in both personnel and reputation. Nobody can question the 6th Brigade's role in the conflict since they were at the front, though they themselves won't be getting any favourable opinions on their way (some might argue that should've died in battle, as is usually the case for those in the front).