I could be wrong, but I now think he saw a clear route through the valley - maybe the same way as he had come. That was poor judgement but at least I can understand why he did it.
That is a subtely different message becasue it illustrates how easy it is even when there is a very simple alternative for pilots to be attracted into flying up a valley.
I suspect this pilot really believed that he could continue up one of the valleys shown in the graphic and over, otherwise I dont think he would have done so. Had the valleys not been there, or had they presented in a different way, I believe he would have "diverted" to the north.
This thread has gone on far too long, but you keep missing a very important point that should be noted. It is
not easy and should not be easy to be enticed into flying up a valley towards high ground in poor weather, even if it looks like you might be able to squeak through. You shouldn't go up any valley, especially in uncertain weather and wind conditions, without at least 1,000 feet in hand at the start to clear the saddle at the top and a clear plan of escape if it doesn't work out.
He made a very basic error in flying towards high ground in dodgy weather and you are complicating things too much. This is an easy and useful lesson to learn from this accident.
Beware paralysis by analysis.