[Vampyr]

They were covering themselves in zombie gore to smell like a zombie. Makes sense to me.

I agree that everyone being infected really doesn't have any bearing on the story at all. I'm not sure if they expected that to be a "big reveal" or not, but it really doesn't change anything, it's just kind of a neat fact about the virus. Maybe it will mean something later on, like creating a "cure" virus to kill the zombies.