The comment was unsubstantive and arguably a bit snarky. Those are downvoteable qualities on HN.

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

I think the downvotes are for the lack of contribution from his comment. It was unnecessary and not on topic.

> Be that as it may why should the poster be downvoted for this?

Because the snide one-liner post wasn't a productive contribution to the discussion. And that would be true whether or not the blogger was prominent.