I think you're missing the point.
Each and every driver is required to be doing a speed appropriate for the circumstances, and that certainly includes the fact that driving at night might reduce that speed, since it clearly often adversely affects visibility.
If you're driving at a speed where you cannot stop within the limits of your visibility, then you're going too fast. Period. End of.
Whether the other cars had lights on, whether wavy-arms-man should have been standing in the road, etc, are all immaterial to the question of whether the driver should have been able to stop, because he should have been able to, and patently didn't. Your work mate SHOULD have been able to stop when he saw there was an obstruction. That obstruction could have been someone that had had a heart attack and fallen into the road, or a cyclist knocked off his bike by another car, or a car with an electrical short that took out his lights, or ..... etc, etc. It matters not what it actually was.
The FACT remains that the bloke that couldn't stop couldn't stop. Ergo, he was going too fast for the visibility .... or wasn't paying adequate attention.
Should the wavy arms man's car lights have been on? Probably. Might he get done for that? Maybe .... if it was actually the case. Does it affect the liability of the driver that swerved? Nope, not at all. He was, quite simply, either going sufficiently fast so that he couldn't stop when he should have, or was not paying sufficient attention so that he didn't stop when (had he reacted properly) he could have.
I can see any escape from either him going too fast, or not paying proper attention .... or both.
It might be fully understandable, and it might well be something we're all guilty off, and if any of us had been driving, we may well have been similarly caught out, but I simply can't see any way he wasn't either going too fast or paying inadequate attention, because the facts as presented don't permit any other interpretation.