I know you are good at looking at the recent activity to know what is going on, but I hope this message explains it.
This category is a little weird, since nearly anthing could be considered a decoration. However, only items designed for decorative purposes (i. e. Flower Pots and Paintings) can really pass as decorations and be added to this category. I believe the polished versions of Andesite, Granite, and Diorite would also be decorative, while their unpolished variants aren't. I understand the description of the category could be a little misleading, and I hope you and other editors now know what to look out for in the future!