Technically, he would not be reflected in the cube that way, since the light would not reflect him at that angle. Light reflects at 90 degrees to the plane of surface. A second unseen mirror surface might reflect that perspective onto the cube we see.
Secondly, the image in the cube should be reversed right to left. Notice that his left leg is bent forward. In the cube reflection, we should see that reversed (same leg but reflected in reverse).
However, it "LOOKS" very believable, which is what is important. It does not to be scientifically correct to be great art.