If you just tried to submit the article, HN detected an earlier post of that URL and just added your vote to it, instead of making a new post with the same URL.
It's grey because you have already visted that URL.
It is missing the up-arrow because you have already up-voted it.
Except I didn't submit the article and I hadn't upvoted it or looked at it yet, which is why I was confused. Thanks for your answers.