It is chillul Shabbos because it violates at least two melachos (probably d’rabanan) AND because it is zilzul Shabbos.
I actually have a hard time believing that they are serious about it (or at least that they had any semi competent halachic expert look at it) because the reasoning is so backwards.
There’s a theory which says that this is an effort to poke fun at left wing “orthodox” reformers, and although I doubt it, I can’t dismiss it entirely.