I walk by this street corner every now and then, and was puzzled by this as well. It's quite different today, but the location is more or less on top of the National Theater railway station [1]. I think you are right about the lens making it look more curvy/steep, in this aerial photo from 1937 [2], you can tell it's just 180 degrees.

[1] https://goo.gl/maps/TNMB6AMVJSA2 [2] https://kart.finn.no/?lng=10.73088&lat=59.91467&zoom=19&mapT...