'Schwarze Kunst' can also be used as synonym for magic and all kinds occult stuff. Maybe because printing was something people didn't really understand back then.
but here I was thinking it had something to do with "blacksmiths are loud" hence we should vanish them to the outskirts of the city cuz they're annoying to be nearby
Despite what the literal translation might make you think, the German term does not refer to the occult. It relates to the art and craft of printing.
'Weiße Kunst', the white arts, apparently refers to paper making.