The Joel character references both of them. After he kills the guy he tells the girl to "Search him. Then take care of his buddy then we quit this place."
Also, there is no sign of infection on that guy. He is just a run of the mill post-apocalypse human doing what most humans would do in that situation. Murder, rape, and steal. It will be nice for a game to really explore how most humans would react to that kind of end of civilization scenario.
Sorry but not everyone would turn into rapist or a murderer. That's stupid to assume. Most of the people would try to reorganize at least in smaller groups and try to survive. This dog eat dog mentality is stupid.