I had the same initial thought when I first read it. I discarded it, however, due to the "a" before "Zum carnival" and the "be it a (this or that)" construction.It sounds like German to me. "Zum Carnival" would mean something like "at the observance of Carnival?"
People in Zumba classes will be wearing batgirl costumes and exercise?As far as I know, "zumba" is an exercise. The word "zumba" was invented for the exercise.
So a "zumba carnival" would be an event that a gym ran for its members. "Dress in costumes and come exercise with us!"