I don't think anyone is inherently stupid. Some are very uneducated, but that isn't the same thing. Some people get by on their looks. By living a certain way. I don't think that's stupid. I just think some people are happy to do that, and don't feel the need to learn anything. But then in their own little circle, they don't need to. Because it doesn't matter whether they know if there are big cities in Australia or not. It doesn't affect them on a day to day basis.
I don't think it's stupidity as much as it is being self absorbed and only focused on their own world. People see vampire movies, where a lot are portrayed as very pale,with white hair (look at Spike in Buffy the Vampire Slayer), and just don't know any different. It's an aesthetic that a lot of movies and TV go for, to portray a life lived without sunlight. However much or little truth there is to it, that's the kind of thing people can be exposed to. It's not hard to make the leap for someone who's never met someone with Albinism and just doesn't know any better.
As for cold weather, I believe it's to do with the physical appearance of Nordic/Scandinavian people, a lot of whom live in colder climates. Being seen as blonde and pale skinned. Again, movies and television have a lot to answer for with this. They push this imagery on people.
This girl sounds like she probably gets a lot of her information from movies, or TV. Rather than actually learning anything. So while it has no basis in reality, I don't think she's being intentionally dumb. Someone I used to work with didn't know how to put petrol in a car. Literally had no idea. Because she lived with her parents and never had to do it. She had no clue what a petrol cap was, and just stared at the hose at a filling station with a completely bemused expression.
People know what they know, and don't know what they don't. I would give her the benefit of the doubt, Julia. In her world, you might not know things that she would consider rudimentary.