From the article it seems that none of these other trips were in deep snow, or that's at least what I deduce from them.

His previous trip was in a very shallow layer of snow. Lesson learned 1: It is pretty hard to pick firewood from the ground when it is covered with snow (not that picking wood from the ground is your best source of firewood anyway, unless it's very dry).
Lesson learned 2: The limitations of a knife when it comes to producing lots and lots of firewood from standing trees. He aborted that trip after a very cold night and promptly bought an axe.

A lot of skills are transferable across the seasons. Still, winter, snow and low temperatures makes for a totally different ball game than the other 3 seasons. You need some additional snow specific skills, and your margin for error are much, much smaller. Not to ignore the lack of gear.

I'm sure he learned a lot from his previous trips. Unfortunately, he did not learn the most important lessons of all: Never underestimate what Mother Nature throws at you.