That was before! It doesn't count
Chester did chopped some heads off and tortured some fellas but then in the prospect of 30+ nobles going off into the world he got convinced by Joran that being a nice Chester might cause some of the poor mind-controlled Xavaxans to join south instead of north.
Then again it wasn't such a lovely idea after all. Chopping people's heads off and torturing them only to provide them with cushions, blankets and full amnesty later on is not diplomatic, it's bipolar. Nonetheless at least a couple more Xavaxans saved their heads thanks to it and a couple more got spared from banishment and possible decapitation at a later date.