I believe the threshold to be able to downvote is 500 karma. You'll also likely be down voted for commenting on downvotes, as it's against the guidelines:

> "Please don't comment about the voting on comments. It never does any good, and it makes boring reading."

https://news.ycombinator.com/newsguidelines.html

As for your original comment, people may have misunderstood what you meant regarding the submitted url.