Here is a different twist. My wife has back issues ane it is painful to sit. At work she has standing desk and will stand all day. Perhaps this man has a bad back and rather stand during flight.
True.
I suspect there must be a physical reason for this photo because as people have pointed out most plane personnel would’t allow it.
Also, why didnt he go sit in an empty seat if there was one. Perhaps he was standing guard over her for some reason