Note: even the lowest level humanoid (capturable) enemies (this includes wanderers) can have stupid high level armor.
Also they can have specializations, and one of those gives armor...
..if (I know this is low chance) they get both the specialization that gives armor AND a strong armor item (HEAVY PLATE) their armor will be enough to bring your damage down to 1, even if you had a longsword and 2-3 strength...