Oh, interesting. I'm pretty sure if you try to take anything from the treasure room they will notice. But I should see why opening the door doesn't make them hostile. Thanks!
They did not. I admit I closed the door behind me, but emptied both treasure rooms. I can run a new save, and see what happens with the door open, however I am guessing that without line of sight, they did not realize.
But I did recently attempt to play via GOG and Dosbox, and the doors themselves are owned, so picking the locks would normally aggro the goblins.
I just loaded up the OG game to make sure I wasn't misremembering. I am correct: Picking the lock or breaking the door open in OG is enough to anger the guard.
In Unity Underground, I can take the food from the barrels without the green getting mad, even break open the chest. Taking from the chest angers him.