Has to be. I collect postcards and anything old to do with my town, i must have a good few old postcards and photos that show similar errors. I even have original printing plates used for postcards that have errors on them!
I would certainly put this down to some error, either with the camera or developing process.
It's cool how you have stuff related to your town. Cool how some of the plates even have errors. I'm surprised they didn't retake the photo or reprint them....