I think he's just looking for a quiet spot to do his business.
He puts me in mind of the Bren Gunner at Pegasus Bridge, whose first act in the liberation of France - straight out of the glider, was to tear off on his own to find somewhere to pee, as he was absolutely busting (one simply cannot pee in front of the Germans, it isn't done).
That is a really cool, atmospheric photo, by the way.