I feel like you misread his comment if you're asking that. His next sentence explains why it's mistaken...

I missed the word new, thanks. Deleted the comment.

Edit: Apparantly I can no longer delete the comment. Stupid HN.

As 'dpark noted, you can't delete a comment once it's been replied to: I believe this is to ensure that there aren't dangling comments. If the comment is still new enough (less than 2 hours old, I think), you may still edit the comment. For example, in this case you could chose to include your note about missing the word new in that comment itself.

You cannot delete a comment once someone replies to it.

Nor should you. It breaks the conversation for anyone reading it afterwards and makes the replies essentially off topic.

...because its not new