I think confirmation bias plays a role here. At the point where I think Bill probably went wrong (of course we will never know for sure), there’s a junction of two basically identical jeep trails, neither of which are marked on the park map or most of the then-current trail maps (they are on the topo map). There’s 3 or 4 different ways he might have gone down the wrong road—others have mentioned the two I put out there, there’s a couple of other ways that are possible but less plausible so I didn’t bother with them—but he should have noticed he was going south and not east, by the setting sun. However, because of the angle of the road and the mountain cover, plus having an obvious road to follow, I can see why he wouldn’t have. The sun would still more or less be setting behind him, and to his right, on either route. If he was focused on making time, it’s unlikely he’d note the exact angle of the sun.
My feeling is that because Bill was in a hurry, he did not get out things like a compass or (maybe, depending on how he got lost) more detailed maps until he knew he was lost and by that time he was screwed by the darkness and the topography of the area which wouldn’t allow him to dead reckon back unless he could find the trail again, and at that point it was a wash, of which there are a half dozen in the area. I basically cover this in the video, there’s a lot of information there so it can be hard to follow, but there are reasons why the compass didn’t get him out of the situation.
It was an interesting puzzle, I like desert hiking, and it was a challenge I needed in my life at that time.
I talk about it a little here (time stamped to the correct location):