There was first a zombie world with a human apocalypse.
Hows this for thought food: Which came first...the egg or the undead chicken that ate it?
Anyhoo, to be clear Sajj, no intelligent person believes in the Hollywood zombie. That's a non-issue. We're throwing jokes around because lets face it, rotting corpses are funny & even funnier still when that face happens to become lunch.
No matter the word used, every culture of every age has their version of zombie mythology because every culture of every age has always had to deal with death.
Rest assured though, there is no such thing as zombies. What there is instead, is simply a broad physical medical condition that the word 'zombie' best describes.
If I were to say vampires really exist because of Renfield's Syndrome (the clinical term for obsessive blood drinking) or some blood or skin disease, that does not mean that vampires actually exist. 'Vampire' is simply the term that best describes the condition to the masses.
What I'm finding funny is that you don't seem to recognize that you and I mostly only disagree on the base point of the definition of 'zombie'. I understand your outlook, but I just think you're trying to hard to justify the term itself.