Photo: Shoveling Ears Of Corn Into A Boxcar (Circa 1910)
A photo from the Nebraska State Historical Society:
Click on the photo to enlarge it.
Unless someone forgot to tell him where the side door was my guess is that he's just toping off the load.
I'm sure this was not unusual but it's the first photo I've seen, excepting lumber, of anyone loading through the inspection/lumber door.