When you quit the game and you have something that causes damage during that turn, the game summary tells you that you died due to the damage, not because you quit prematurely. E.g. a mist elf in full health but wearing something of iron quitting will get the message that he was burned by the poisonous touch of impure metal. My guess is that quitting pulls your HP to 0 internally and then, related to issue 6004, the last damage-dealing event is populated.