It's very much a dupe by HN's rules of dupery. It's just that saying 'dupe' went a somewhat out of style since it can come off a little aggro. 'Past discussion' is often just the polite way to point out a dupe.

On HN "dupe" means "the story has had significant attention in the last year so. This is in the FAQ: https://news.ycombinator.com/newsfaq.html.

That doesn't mean it's a bad submission! it's a good submission, it just has also already happened recently.

Agreed, but on the other hand it's the 3rd time I'm seeing this posted and there's no new releases or anything.