Here is what I think happened.
He accidentally clicked the NPC NEXT to the stone. This NPC has the donate option.
On the EC client it can be a bit funny when typing numbers in because all chat goes to the same box. I think he typed in a number and hit enter, thinking he was retrieving held gold. (User error no doubt)
Now the BUG, from when I looked, seems to be that ANYONE can donate to any person. The gold goes nowhere though, as you are not a citizen. Should it not block you from donating gold, if not a citizen of that town?