There is an existing question How is it possible that a single user who is not a moderator can delete a comment? 4 years old about a post a year prior, that focuses on a post containing the word(s) 'accept', 'accepted' and/or 'accepting' I do not believe this is the same.
I am a 10k+ user on a beta site, saw a new post that was not a good fit, down voted it, voted to close and left a comment while the view count was at 2. I moved on.
The OP posted a comment and I came back when I got the notification. The comment contained profanity and I flagged it as Rude, and the comment instantly disappeared (screen shot above is after it disappeared)
I looked at the Privileges page and it does not seem to be a documented feature.
How did a non-admin delete a comment with a single flag?