A different type of reward dropped from the pack.

Having achieved 500 kills on the Peacekeeper, while having all the conditionally free skins (1200 metals each), I opened the Peacekeeper set given for completing the challenge (for 500 kills). Having opened it, having all the skins (free), I received not even close to the Peacekeeper, the Legendary skin for the Seer dropped, which is fundamentally not like a shotgun.