That could very well be the case, especially if there was some sort of reflection in the glass. Unfortunately, with the distorted photo you really can't tell for certain if the figure of Piper was behind the Prayer Man. But if you look closely enough, it appears there could be something next to the Prayer Man's left arm in the background.
Yes, Mr Plant, if one goes through frame by frame, then there does appear to be some visual information there behind the glass that
may be lending illusory volume to Prayer Man's body............
e.g.
Some have suggested that this is Prayer Man's reflection in the glass, but I'm not sure the light conditions are right for that........