It seems like the hikers were otherwise prepared.
After watching the video of how the events unfolded, I don't think that any of the hikers were actually prepared.
Firstly the group essentially panicked, firstly by the overnight snow and the assumption that they were just about to washed away in a flash flood. This assumption that a flash flood was likely was basically unfounded considering the weather conditions of lying snow and sleet later in the morning.
Secondly they left some of the most important gear behind in weather conditions which would have saved them if they got into trouble making their exit. They would have perished from exposure that night, where they ended up, not having had the good fortune that someone saw the commotion on the side of the hill.
Thirdly, the group leader most likely could not read the terrain contours on her map and stuck to the compass bearing blindly to reach the intersect with the road. i.e. did not recognise the contours were getting closer together on the other side of the hill/ridge they had to traverse, i.e. they should have detoured around the obstacle, even though it would have been further to go. There was a lack of ability to think in 3 dimensions. It must have came as a surprise that the hill became steeper and steeper as they descended down the hill. They failed to recognise that they should have turned back and found another way down even if it meant going back up the hill once more. But probably by this time arguments, recriminations and emotions would most likely got the better of the group dynamic with some probably refusing to budge deciding to risk other folks lives in a rescue if they were eventually discovered on the side of the hill next to the highway.
If these folks had perished on the side of the hill only a few hundred feet away from the road, the mystery would have been how they actually ended up where they did and the irrational logic behind their incompetence.
I guess it goes to show that if you rely on someone else to do your thinking and navigating for you, you have no business getting upset when you get stuck on the side of a 'cliff'/sleep hill when deferring those skills to others.