Are we supposed to be seeing a person in the background? I can kind of get a figure if I squint. Looks like a simple case of pareidolia. I was already skeptical just reading your post, without even looking at the picture, and here's why:
According to him, he had not seen anything behind the workers when taking the photo.
That pretty much tells you right there that the phenomenon is going to be an artifact of photography, either what we have in this case, which is an artifact of converting 3D into 2D in a very blurry way, and then letting natural human pattern-seeking take over, or something like flash artifacts, which are what cause "ghost orbs" and streaks of light in pictures.