So, coming from an anthropology perspective - Lots of things are religions. It's not a big deal. Chicago School economics is a religion. Liberal economics is a religion. Marxism, scientific or not, is a religion. "The Revolution" is an eschatological conflict at the end of history, at once immanent in our lives yet also constantly occupying the horizon of time.

Something being a religion doesn't comment on it's moral qualities or truth value or whatever, it's just a descriptive term. And Veganism, with it's distinctive beliefs, moral code, dietary restrictions, cultural markers, etc etc etc, counts.