No it just means Mary was a goy. Luther said Jews "do not stop blaspheming our Lord Christ, calling the Virgin Mary a whore, Christ, a bastard". Mamzer has it's roots in Jewish law, which in general is against integration with other cultures where we don't consider someone Jewish if the mother isn't Jewish - it's the opposite if the Mother is Jewish and the Father isn't. This stems from the resistance to Hellenization earlier from the Greeks that led to the Maccabean revolt. It was the lack of integration/conversion that was concerning for Luther.