I've left a comment on this answer explaining why I have downvoted it and how it could be improved. Other user replied, I replied and the comments section eventually got too chatty, so all comments were removed (which was a right action IMO).

I thought that the first comment could still be useful for answer's author, so I've flagged the answer for moderator's attention, adding a message:

I left a comment on this answer explaining how it could be improved. It seems that it was deleted.

The flag was declined with a message:

No idea why you are flagging because a comment was deleted.

I'm quite confused. I didn't state explicitly that I think the comment should be undeleted, but I thought it's clear from the context. What should I do to let moderators know that I think a comment should be undeleted?