I wonder how I did that.

If you click the "Create new article" button from the main page, you get a "post to" drop down that lets you choose to save to your drafts, to Less Wrong, or to Less Wrong Discussion, with your drafts being the default. This is probably what you expected.

If you click the same "Create new article" button from the discussion section, there is no drop down, and you always save directly to discussion. This is probably what happened.

(I think this difference in behaviors is unnecessarily confusing and should be removed, by making discussion act like the main page.)