A metal plug with metal tabs locking behind the plastic ears on the oil pan sounds like a recipe for accelerated wear at the minimum, and chipping/damage at worst which may explain how it came off.The UPR one has the same thing. You have to use a flat head screwdriver to pull up the tab so it clears past the pan slot then you can turn it. When you screw it on, it snaps down in the slot and can't be moved without prying on it.
Unless this is an old design plug, I can't imagine what would cause it to come loose. It has the same exact locking mechanism as the stock plug, only difference is it's made of aluminum vs. plastic. Something else must have happened to the plug, maybe the locking tab was fatigued and failed allowing the plug to spin and pop out.