Yes, this is unintuitive and a bug, you have to start writing articles from the main site to have an option of saving to Drafts, there is no such option in discussion area. But not working around this bug results in spurious articles appearing in the feed, hence it's a posting "by mistake", but the kind that can be avoided, and should be. This is the same kind of mistake as using HTML markup in comments - something that can be reasonably expected to work, but actually doesn't, so has to be taken into account before posting.