"One of your uploads has been deleted: zyx6yw Reason: Broken rule (collage)"
But there is no general rule against putting two pictures together, unless done poorly (cobbled together, as it says). While certainly no work of art there was some effort done with putting these two pictures together and touching them up, in order to create and actual wallpaper. If the upload still falls under the "low quality" rule then I guess that's so. I'd actually look forward to an improvement to the average quality among accepted uploads.