[I] That's not a distinction I saw in my googling/dictionary checking, but it's an interesting idea. Mind you, at this point Superman certainly has multiple authors as well.
[GL] My bad: I think you're right. It is pretty clear at least that Superman is not an "obligate carnivore" (a term I just learned, meaning solely flesh-eating). And given that I also saw Superman eat a bomb in another episode, "omnivore" seems more appropriate. Googling seems to indicate, however, that the strict definition of these terms has to do with the necessity of different types of food in terms of nutrients. I actually have no idea if Superman has to eat anything.

[Rosie]British - Yes
[irach] Scientist - No