From top to bottom is 90 degrees, and from side to side is 0 degrees. Therefore, since the slope goes more top to bottom than side to side, it's closer to 90 degrees than 0 degrees.
Wow....the person who captioned this photo is an effin dumbass. Awesome shot, great photography, and stupid-dumb-as-hell logic. I wish people were just smarter.......
Read a geometry book.