If it is indeed a boneheaded mistake, then it’s probably because of over reliance on RPC-type calls from the front-end that displays the data, to the back-end that actually handles the data. User deletes photo, and the front-end, instead of actually deleting it, tells the backend to do it… and then hides the photo from view, maybe updates its index of photos marking them as “deleted” regardless of whether the backend actually deleted the photo.
Then an OS update comes along, and rescans the filesystem, and report a bunch of new photos to the front-end, that then happily add them to the GUI to the user’s surprise.
Modern APIs and software architectures are a bloated, unnecessarily complex mess, and this is the result.