Does anyone else see a connection between the armor and the worm in the smoldering lake? The Pilgrim Butterflies look like something born of chaos, so in the worm. The worm uses lightning, as does the armor (I know, many people use lightning, but this ties in with my final point), the worm drops a miracle that was once used by a great dragonslayer. That armor and that miracle are the only two things associated with dragonslayers that isnt really known to be connected to Ornstein or the Nameless King. I know some people theorize that the worm is Solaire, but he was not a dragonslayer nor used that miracle (he used Sunlight Spear, not Stake).
It's not much to go on, I know, but there really isn't much to explain that armor.