Free win for the Ultra Greed fight?

I got to the Ultra Greed fight with one heart left, he spawned and then just immediately died and the fight was over. I don't think I even fired any tears, he just instagibbed. I'm grateful for the win, since I wouldn't have won otherwise...but umm, what the hell just happened? Did it glitch or is there an item combo that might have caused this? Has this happened to anyone else?