Not your fault, that place is a accident just waiting to happend.
To many candles lying around.
I did this on purpose the other day. After taking out all three of the main baddies at the Goblin Camp, the trader and the two rando elven archers retreated into the alcohol barrel room. I decided the quickest way to deal with them was to back the rest of my party the fuck back, gulp down a potion of fire resistance, and then let an arrow rip.
One long rest later, the trader's entire stash was mine.