ImzFrozen is correct.
Enemy weapons seem to have a bit of a random chance of dropping, but you can almost always influence whether or not an enemy’s armor will drop. Use flails (with the strike head ability) if an enemy’s head is exposed. Otherwise, like on this first encounter, you have a knife. A cheeky way of obtaining a piece of armor on this level is to have your archer switch to his knife, then have him use puncture on the enemy that has the armor that you want. Don’t worry about dying, as it is impossible for any of your guys to die on this first encounter.
"It is not death that a man should fear, but he should fear never beginning to live." ~Marcus Aurelius
Game: "Characters with a height advantage against their opponents are harder to hit"
Me: "That's not true, and my short axeman is living proof!"