I believe your assumption is correct. "Zombies" are commonly used as a planning and training substitute or generic cause when no specific cause of disaster is stated. For example, I recently completed CDC training on distribution from the Strategic National Stockpile (of antibiotics, antivirals, vaccines, anti-radiation treatments and other disaster medical supplies). We used a "zombie outbreak" as a generic causative event, including targeted medical screening with questions about, e.g., rotting body parts and a recent appetite for raw flesh.