it somehow a bit derived from the npc events in fo2.
faction who seek for pvp are able to activate teamtracker option in faction terminal. so when a defined numbers of members are as a group somewhere (reno..wh.. signal flare encounter.. etc) npc start talking like "faction xy is killing people in reno, someone should stop them".
while activting/deactiving this pvp teamtracker in dialogue it is up to the faction if they want to be found or not (want pvp or not)..