Killing merchant in act 2

I got three rancid potions from an event. The description says that throw at merchant to get 100 gold. Then I entered the next question mark and got a Merchant??? that is only selling a potion and a few relics.

I threw the rancid potion at it and it got pissed. After killing it I got all of the stuff that he was selling and 300 gold…. Slay the Spire 2 is amazing