The wine was labeled "rot" because that's the German word for red.
At the end of the OP, Subaru says "This story is a work of fiction," and then Kazuma adds "Please use as directed!"
I don't know if the lyrics change later in the season or if it was just the translators having fun, but in the English cover of the song Kazuma's line becomes "Shippers, go nuts! Give money, receive isekais!"