So what... it means it has to taken from the Metallica song, not Bowie?
In fact, Ziggy Stardust was made more than a decade before Leper Messiah. Its always very, very possible that Metallica took the name of the song from David Bowie. Not like its an uncommon practice. If that's the case, then ultimately it means Leper Messiah draws his name from Bowie, even if that wasn't the original plan.
Oh...
And David Bowie>Metallica :-p