It's not just a wallpaper, it's general execution, because these things are intended to be able to add general functionality. They can add a menu item to variou

It's not just a wallpaper, it's general execution, because these things are intended to be able to add general functionality. They can add a menu item to various menus and provide code to execute the new menu, and that's the goal. You can make a program that sets a wallpaper and write a description, "download my free wallpaper", but that doesn't make it into a wallpaper, it's still a program. The KDE store doesn't have a category for non-programs.