Zombies can regenerate parts, which means they constantly retain a sense of youthful vigor. This also means they live significantly longer than humans. The average lifespan of a zombie is one hundred and fifty seven years. It is no wonder, then, that humans see this and assume that they must be the walking dead. I suppose a fly, with a measly one month lifespan must think you are a zombie as well. It’s an issue of perspective and proportional reasoning.