Brown "polar bears" are called Grizzly bears. For the most part they drowned in the cold water. Polar bears have many more adaptations than the pigmentation of their fur.
I agree with many of the fine points made by the people I pinged and others particularly about the oddity that the Inuits as a group seem to violat the furhter north the lighter rule, perhaps due to their diet being high in vitamine D.
In some ways I view this article as anthropromorphizing. These humans were just on the cusp of survival their entire lives. They likely were not all that picky about what they ate nor where they spread their seed. The latter being something many woman claim has not changed to this day.
I can offer an amusing alternative hypothesis to near starving, short life expectancy cave men perferring blonds, waiting around for a blond to walk by and risking not procreating. As we all know we fair skinned people do not run as fast, particularly in sprints, as our dark skinned brethren. So perhaps blonds were just slower and caught more freqently by all males? And that would explain all the dumb blond jokes as just a misunderstanding of slow and dumb someplace a few 1000 generations back?