When looking through a camera’s viewfinder from the ground up at a building, there is distortion that occurs. This distortion causes buildings to look like a triangle.
There are multiple ways to correct for this, including what’s called a tilt-shift lens and also perspective control within photo editing software.
Sometimes, however, there is no reason to correct the distortion. Simply because the angle the building is photographed is interesting enough to work as it is.
This is one of those times.