It's a joke. An urban legend around the area, about a man who lived in the woods, wore a mask and was immune to zombies.

[A silly little joke, and somehow Jack has been so prescient.]

The fast ones are fast. Shamblers aren't so bad. The ones with machine guns and rocket launchers were awful but thankfully seem to be dying off.

And then there's the semi-sentient ones, and the indestructible thousand year old viking zombies. Nasty business.