Scheduled Posts not totally private (Security Issue?)

I recently created a scheduled post that is to be published in the near future. When looking at my 404 logs (through the Redirection plugin), I noticed a hit to the preview of the scheduled post coming from an IP address that was not my own. The URL is unique and not likely to have been guessed – and the IP address that tried to hit the page (they got 404ed) is an affiliate marketing company on the West Coast. My question is how they knew anything about the post or its title in order to try to access the page? Any thoughts would be appreciated.