Here's my shot in the dark: Since we know that the time period could be ~1935 (golden gate bridge construction), and the zombie eyes are red (Samantha nor Richtofen can be in control), so maybe while in purgatory, we are the ones in control, influencing the zombies' motives and controlling the game. Purgatory does sound an awful lot like the aether, maybe a theory is that the influence happens when the controller is in the MPD, a possible gateway to the aether, also known as purgatory while controlling the zombie?
I'm not sure. We'll have to wait and see, I guess.