Also why doesn't anyone use the word: "Zombie" in this series. Has Disney copywrited it?
Eh, doubt it. Most likely, it's just the same conceit that every zombie movie makes: almost every zombie movie takes place in a world where zombie movies never existed. Bites, shooting them in the brain, it's new and novel concept every time.
With the notable exception of "Return of the Living Dead", where they knew all that stuff, tried it, and it didn't work.
"I thought you said if we destroyed the brain, it'd die!"
"It worked in the movie!"
"Well, it ain't working now, Frank!"
"You mean the movie lied?"
Although that movie made the zombies so unstoppable that it's hard to see how the original outbreak was ever stopped in the first place. Did they establish any way that they actually could be killed? I haven't seen the movie in a while. (Yes, I know it's a satire, but....

)
Yeah, I don't recall though if zombies exist in popular culture or not in the context of the comic, however.
I like the way the series handles it though. Because, again, if zombies don't exist in popular culture then why would the word itself exist? And if zombies DO exist in popular culture then certain tropes, like shooting them in the head, not letting them bite you, etc.; would exist and be known.
The word "zombie" would still exist in reference to the original voodoo-style zombie, so no problem there. It just never made the leap to apply to the walkers. You'd think it would be obvious, but as you say, Romero himself didn't even do it. I think that started with Fulci.
But you're right that there was no such thing as a Romero-style zombie in the popular culture of that world, even under a different name.