Very much this.

I live in Norway. While I'm below the Arctic circle, summer nights are bright. I don't need outdoor lighting to read as the sun goes juuuust below the horizon. This time of year, days are short and the light intensity never really gets all that bright. I don't have issues with any of it - and I'm an immigrant.

There are many genetic differences, even within a given ethnicity, concerning sleep. What may impair sleep for one individual may have no effect for another. This variation may have been beneficial from an evolutionary standpoint, because variable sleep schedules meant that someone in a given community could always respond to threats.