The post in the audit was the accepted answer. You flagged that answer itself — not a duplicate answer, since in all likelihood no such duplicate was ever posted — and, of course, if it had been a live review flagging a good accepted answer like that would have been quite wrong.
How can this be? Well, audits will deliberately fake post details so you can't tell if a post has been accepted or upvoted, or who wrote it, in order to avoid making audits absolutely trivial: you have to look at the contents. But this means that naive attempts to suss out duplicate answers will get you in trouble when simply not looking for duplicates may not.
But all is not lost: if you pay attention to where you land on the page when you click the link to the right of the answer in review, you can always tell. The link given will always scroll you to that particular post; if it leaves you at the top of the page, you know it's been deleted (and is therefore a known-bad audit), and if it takes you to an upvoted answer unexpectedly, you know that that's the real deal and that the review is a known-good audit.
P.S. Looking for duplicate answers is very helpful, so please do keep doing that, just make sure to look at all the information available so you don't run into audits.