I'm not seeing any witness marks on the failed joint.. can you point it out please? Are you referring to the galling inside the nut seat?
The witness marks are the thin pattern on the face of where the nut would seat against the spindle. This does not mean the nut was even tightened. It does show that it was there but not necessarily tight. If the nut was even torqued at all there would be witness marks all the way around the face of the mating surface of the base of the nut and the spindle.
The design of having the ball joint nut facing towards the floor helps prevent the car falling when stuff like this happens. Not say its ok at all for this to happen. If the control arm met the spindle from the bottom with the nut facing the sky as soon as the nut came off then the car would have dropped to the ground.