From looking at both pics, it would look like he's wearing the cap front forward and it simply doesn't have a bill. If you look at the broader picture, all the other caps appear to be the same style and the back seam of the caps are a lot longer than the front and the buttons on his cap appear to be in the correct place.
What I see behind his head to the left (his right)is something stuck to the bottom of that boot, and the bottom of the bench that the gentleman directly behind him is sitting on.
It would be very unlikely that a soldier would alter his uniform in a way that could draw reprimand from the CO, if left unchecked that would be detrimental to unit discipline, but what's he to do if he was issued a cap without a brim but wear it?
That's just my take on it, but it not one that's without experience.
That's a good eye though. Looking at the bigger picture, I'm not sure if I would have picked him out of the crowd.