This happened on this particular First Post review, I cannot reproduce it because review audits in "First Posts Reviews" don't come up very often:
The post (an answer in this case) is clearly weak, this is a general agreement since it is a review audit. I was reading the question below the post being reviewed, and clicked the "See more comments" link in the bottom of the question. As soon as I clicked, I got the "Congratulations, this was an audit" message.
I was just checking the question, I hadn't taken any action on the answer that was to be reviewed yet. It seems like any action will trigger the audit response.