That is a tough one to call.
Because we are apparently looking through a glass door at an angle it is very hard to break down what is in the room and what is a reflection.
First a similar dark shadow appears at floor level (see attachment). I would not have even noticed it if I had not been trying to work out all of the artifacts.
There are three artifacts in front of the shadow that seem to be reflections or glares. The white glare at the "arm" of the shadow, the greyish "curtain" that one could say it is partially behind, and the last is a bluish area that obscures where its feet would be. Because of the these artifacts, the origin of the shadow is brought into question.
I suspect it is a reflection. However, it is definitely interesting and look forward to reading what others have to say about it.