swedish/norwegian language

Ok just out of curiosity, in the movie when Jonas would speak swedish to some of the characters (ex; the classroom scene, and also in the interrogation room to the girls boyfriend) It was brought up that they didint understand him. also that the only reason Tanja understood him when he spoke it was because she had been around swedes before or something?
Now I speak or understand neither, but I was told (by a norwegian speaking norwegian lol) that swedish, norwegian and even danish were mutually intelligible languages. So once I saw the movie and heard this it kinda confused me. And maybe Im missing something here, but either way, if someone could help clarify this up for me that'd be great, thanks!