Offering Ritual Seed Nursery to Bishop gave Automaton's Potion, not Charm Oil

Following the long (and, to be honest, quite tedious) quest line to avoid killing the various monsters for their loot, I offered the Ritual Seed Nursery to the Automaton Bishop, but instead of the expected Charm Oil, I instead received a seemingly rather useless Automaton's Potion. From what I understand, imbibing this potion supposedly makes them non-hostile, which seems pretty useless. I have no idea how to complete the quest in a non-hostile way, except maybe crafting another Ritual Seed Nursery and trying again I guess. Or, simply give up and kill an Automaton Bishop. That's what the game seems to really want me to do.