Herbivores are reciprocal to omnivores. Vegans are not comparable to either. Vegans don't eat animals not because they can't, but because of their beliefs. The word vegan describes a belief, contrary to omnivore and herbivore that describe physiology.
A human may choose to walk on all fours because they're insane, but they will still be a biped.
A human may choose to walk on all fours because they're insane, but they will still be a biped.