When I went through the challenge voting, I didn't notice the strong symmetry. I just saw the side benches. Looking at it again it really looks like the symmetry subject is more about the metal frame. I think I might have missed this at first glance because the picture is bottom heavy. Not sure why I didn't really see the strong correlation before. A terrific image.
There is one thing that my professor taught me that I'd like to share. When taking pictures of benches, wheels, etc. be sure to include the stability of that object to the ground. In other words, the legs to the bench should be in the photo, or else the benches look as though it is floating.