Board Thread:New Features/@comment-1807002-20151126003823/@comment-4731443-20151126030654

Let's see... Looking at your Main page history, that category appeared on August 25. The only template added then according to the diff is clrl. Guess what I found there :)

Edit: More accurately, I don't think the category was added to the Main page on August 25, but the categories in the diff's preview probably appear retroactively. The responsible change to clrl is dated from yesterday, which fits with the circumstances you described.