if you loot the car he tells you clem is wearing his son's hoodie.
>his son's hoodie
what male child wears a pink hoodie???
I think what happened was campman ambushed whoever was really in the car, chased them into the woods, and killled them. He then cut off one of their heads and put it in a bag to be his "wife". That's why the keys were still in the ignition for the car. It was more than likely a woman traveling with her daughter(who ended up becoming his fake family in his mind). If you check his story it makes no sense. Why would he leave his car opened and unlocked with the keys inside it to go HUNTING with his kid? and why would he go hunting when he already had food? in the middle of the night no less.
yeah, he was just a psychopath.'
EDIT: apparently the looting happened while he was searching for his son. Even still my point stands that it all never really happened in the first place