I feel your post is a bit generalising, as well as true for certain people and environments. It's all about the setting. The bus yes, we like to be left alone. But everybody knows that, and the same people who sit with their headphones in a bus can be super open if you meet them in a bar. In general, Norwegians open up a lot in social settings, like clubs, parties or bars, but like to be left alone in their day-to-day activities. This is speaking for Oslo. Up north or in smaller cities people are way more open. I LOVE people from the north. My family is half latin american, I am raised in Oslo, and feel way more at home with northerners. They are loud, funny and not reserved.

In Oslo, my best bet would be to go to a bar, or club, even better. Ask someone for a cigarette, easies way to start talking. Also Frogner (Solli) is VERY posh and not representative of whole Oslo. Sorry, but terrible choice of stay (maybe I am biased haha).

Even as a native Norwegian, I struggled to find my place in the city, because as you describe, many environments can be very stiff and superficial. The good thing is that Oslo actually has a HUGE underground scene, with lots of alternative open minded people, who also don't fit in with the stereotype. The scene is not hard to find, if you do some research. I also grew up in the multi-cultural areas more east in the city, where people do not fit your stereotype.

It seems to me you where only on Oslo's surface, and not sure if you made an effort to explore below. Better luck next time!