Right but there are lots of ways to test problem solving skills that don't involve asking people to both solve a surprise (and obscure) problem and come up with code at the same time whilst under stress. The latter three things are probably clouding your results in a way it's not really possible to account for. It seems like a lot of people setting interviews lack a bit of empathy.

The grandparent seems like the problem solving equivalent of yelling "think fast" whilst tossing a basketball at someone's face to test reflexes.