Ok, that leans it in favor of the father.
The clincher is, given the situation and layout of the road, had a non drinking driver approached this scene, would they have had an accident?
A reasonable and experienced, sober driver will not outrun his vision. This means that at night, or on a winding road, you drive only as fast as to stop in front of an obstacle that you just saw. Around bends you drive always assuming that there is a boulder on the road, or a bicyclist, or a deer - you should be able to stop in time after you see the problem. I also saw chickens on the road, and pheasants, and wild turkeys, and people riding horses, and hikers on foot, and a cow; one time I turned around a corner and saw a line of stopped cars - they were there because of an accident ahead, and the road was blocked; the only LEO in charge had no traffic cones to warn drivers before the bend.
This means that a good driver typically wouldn't have the accident regardless of what is happening on the road. But I would make an exception if the victim intentionally reduced their visibility, beyond what is reasonable. For example, if the taillights are off at night and covered, so that their internal passive reflectors are also inoperative, and the truck is painted matte black. In this case only an investigation can tell if an average driver with an average night vision could be expected to see the obstacle in time to stop.