The chocolate seltzer water probably is plant-based. The ingredients just say, "carbonated water, natural flavors". That would be funny if someone had a drink that has a non-vegan natural flavor and having them drink it. It actually wouldn't be funny at all, an asshole move, actually, like stabbing someone to death at the Petworth Library.
It's really good, though. Kind of expensive but one can is definitely worth it. The orange sherbet (which I used to love when I was allergic to milk as a kid) wasn't worth it, and there was another flavor, I think something I hate like watermelon.