Prez wrote on Dec 19, 2012, 22:13:

... It's nothing more than a cheap knock-off....

There is probably no way of verifying either way, but Titov claims the War Z was in development already by the time the DayZ alpha released. Of course, given how they weren't too worried about honesty in what was reflected on the Steam store page, I know I am less inclined to believe Titov.