Well Sean mentions that Randy & the water techs have left to the pumping station so obviously he's still normal at that point. Yes Randy is later seen as a zombie and is recognized by Michael. How would Michael know his name or recognize him? Speculation draws us to think that they met at the pumping station while Randy was normal, and at some point during the escape wether Michael witnessed it or not (he said the events were "horrific") we know Randy gets zombiefied and joins the horde.