It is possible, but unlikely, that the film was loaded incorrectly into a 35mm camera. I can't think of a 35mm camera where it would be possible to load a 35mm film roll upside down since the camera housings are designed to accommodate the film roll and the flange on which the film is made exits the film. Inserting the film upside down would make it impossible to close the camera and should immediately raise doubts as to whether the camera was inserted correctly.
However, it is possible that the film roll was used with an adapter in another non-35mm system, such as a 645 medium format camera. Depending on the external system used, it may be necessary to wind the entire 35 mm film on a secondary spool and then shoot backwards along the orientation of the film. In this scenario, a 35mm film container may be loaded upside down if the spindles do not care about the alignment of the grooves in the spindle of the 35mm film container, or the entire assembly is (also) reversible possible in any system that carries a film back that can be rotated 90 degrees on both sides of the vertical). If your negatives have an image exposure in the edge of the sprocket hole, it is very likely that they were shot this way.
Another possibility is that you work with APS films instead of 35 mm films. APS cameras reel the entire film on the camera down to the last available unexposed image in the body. This allowed APS camera users to take a single image and swap the roll for another roll (usually to change the ISO).
Finally, if the orientation of the prints is turned off and they were made with properly wound negatives, the person who printed this print series only reversed or misaligned the negatives. In any case, if you have the negatives, you can scan them again or have them reprinted with the correct orientation. The only likely additional problem (besides the technique of the original photographer) is a slight loss of sharpness and contrast in the captured images caused by the wrong side of the base.
PS. If the negatives came from a self-contained unit, such as B. a disposable point-and-shoot camera, there could have been a bad batch where the film was reversed and rewound. I don't know anyone who came across it, but of course it's not impossible. Given that many of these cameras have been used for 4×6 prints, it is possible that anyone using such a camera may not have noticed the result or made any noise.