He'd be wrong though. It's fair for him to claim there are no Romero films or anything inspired by them but it'd silly for him to imply there are no voodoo zombies. So there are old zombie movies out there like White Zombie and maybe even current films like The Serpent and the Rainbow. People in this world might know the word zombie but the simple fact is that these creatures are not zombies, they would more likely be called a ghast or ghoul, perhaps a revenant or a dozen others names from the old countries.
But it was Romero's films that equated the term zombie to reanimated corpses that feasted on living flesh (even though the films never used the term). Prior to that, anything that was zombie related, including
White Zombie , those zombies didn't eat people, and they were just mindless automatons (and in both the films you mentioned, the zombies were what's considered "living zombies", basically human beings that appeared to be dead, but weren't, often depicted as no longer being who they are) that were being controlled by humans through voodoo to do their master's bidding. So, without Romero's films, people wouldn't have thought of the term zombies to apply to the Walkers because zombies eating human flesh was introduced in
NOTLD. But the irony is in the first three films, there was never a mention of the word zombie, though voodoo was mentioned in
Dawn of the Dead in the iconic dialogue given by Peter.
Without Romero, the term "zombie" wouldn't be used for the Walkers because Romero's films made the word "zombie" well known (especially in the U.S.) AND associated with dead corpses wanting to eat human flesh, much like how
Return of the Living Dead associated the term "zombie" with dead corpses that wanted to eat brains. Think about it like this: let's say the Romero films never existed and you live in the U.S. (which I'm hypothesizing that you do anyway), do you honestly think you would know the term "zombie", let alone associate it with corpses that have resurrected and eat living flesh? Even more so, would you honestly know such creatures as "ghosts" or "ghouls" if you weren't familiar with those terms? You probably wouldn't unless you were studying Voodoo or were from those old countries to use those terms, and would probably use terms you're familiar with to associate with them, much like many of the characters in
The Walking Dead do ("Walkers" because they're walking. "Biters" because they bite. "Geeks" because of canival performers who performed wild or disgusting acts, which often included eating living things while they were still alive).
So, Kirkman is right about the lack of the word zombie being used in the story, especially in the U.S., because Romero's films pretty much made the term zombie such a well known one through association, as well as made the zombie genre as we know it now the way it is. Without
NOTLD, the term would only be in use by Haitians, people studying ethnobotany or ethnology, or are someone who practices Voodoo. And so far in the shows, none of the characters fit those categories. So, no use of the word zombie by U.S. characters because there was no Romero
Dead films to associate the word with and leaving them to come up with their own terms, like any one else would in that scenario in their own countries.