It's not that it's a repost; it's that it's mostly reporting on the content of another article. In such cases it's standard HN practice to prefer the latter, as the guidelines say (and have said since ancient times). It's not that you did anything wrong! and I'm sorry, I know it sucks to have an article doing well on the frontpage and then plummet for no obvious reason. But from a mod practice point of view this is a pretty clear call.