So this happened

I got the quest Repair Fog Condensers at the Visitor's Center. So I am watching this guy's back in the parking lot, while back at the center I hear hell breaking loose. The whole time we are repairing they are shooting. So we got done, and I am joining the fray. First thing I see is my Red Vim armor running by me, shouting with Nick Valentine's voice. I did not tell him to do that. And the armor had no core in it. The second thing I see this bolding leather armor clad settler swinging my Atom's Judgement at some gulper. The third thing I see is all my dead bears, gulpers attacking en mass, a legendary glowing wolf, and an enraged fog crawler to boot. That's what the settler mean when he said "You never know what can come out of the fog" I guess. So I go to work, gulpers check, wolf check, crawler check. But the settlers continue shooting. Finally I figure out that they are fighting the caravan guards. So I off one of the guards to quiet everyone down. It works. The rest of the guards, still red and the bolding guy with my legendary quest hammer, who is none other but Lucas Miller, is also red are at the trader's post a little ways off, and out of settlers' agro range. So I off Miller. Who goes on the ground, does not die, and then goes green. And the whole thing is copacetic. EXCEPT. He still got my hammer. I barter, it's not for sale. I take him behind the trader's post and shoot him in the head. He's down. TA-DA. He's got my legendary on his corpse. And just then, Nick in my Red Vim armor peppers me with grenades and the kneecapping laser gatling I gave him. I go down. Now I am afraid to go to visitor's center.

TLDR: A trader stole a weapon from the workshop, aggroed the settlers, and generally bugged out the game.