Since there was a condition for killing only 8 enemies, maybe enemies killed through brawn don't affect kill count.
In my playthrough, I put a lot of points into brawn, wits, and agility for the skill checks. This meant I had to get rewards from areas I was severely underpowered in.
My solution was to just run from every enemy and hope for brawn kills. My instakill chance was always around 40%, and my flee chance was around 75%. That means only about 27% of my kills involved actual combat.
I should've known this game's an oldie. It reminds me of Oddwarg's Animal RPG.