I'd wager it's called Platinum for the same reason Iron Pyrite(sp?) is called Fool's Gold. You could probably fool someone into thinking that it's Platinum. Either that or the 3 Anima used alter the properties somehow, but these are simply guesses.
This was my first guess. It is called 'Rogue's' platinum afterall. They've already confirmed that this is the right recipe, but I figure that this is the reason for the name.