I think that a shadow has as much "weight" as the real thing, especially in black and white which is sort of abstract to begin with. In this case we see the real against the unreal, the light against the dark, and the vertical against the horizontal. Think about it, which is "more real"....the dark, weighty tree shadow or the lighter, softer side of the old building?
One of the great things about the art of photography is that we get to choose how things are expressed and to some degree how they are experienced by the viewer. They may not always agree with us due to their own background, training, and viewpoint but the goal of causing the viewer to respond is a worthy achievement. The type of response is less important than the act of response. To receive a response, any response, is to have touched the viewer in some way and that is one of the goals of art.