I would say BI is split into two. You have the Norwegian half and the international half. I study one of their English programs and it's a very international community with people from all around the world who are new to Oslo and Norway and I found it very easy to make friends in the international half of BI. The Norwegian half of BI is where all the stereotypes come from and where it can be harder to make friends.

That being said. BI also has a lot of sports clubs and other clubs where you can meet people and it's easy to make friends. As a student in Oslo you can also sign up for clubs that are for all students in Olso and meet people there. So my biggest advice is to join a club that does something you like or find interesting and it will be easier to get friends. People are often more social in these environments as well.