TL;DR: You can't undo your review but, if appropriate, you can still flag the post.
If your review had removed the post from the queue, but you had manually cast an NAA or VLQ flag on the post, I believe that would have put it back in the queue.
However, you should only do that if the flag you are casting is really correct for the post. Often NAA is appropriate for posts that should be deleted, but not always. Occasionally VLQ is appropriate, but not usually; there aren't that many situations where the VLQ flag is considered correct.
For That Particular Post
Here's the post's review history. About eight minutes after you posted this question, I cast the third delete vote on that answer, which deleted it. (Following your lead, I also voted to close the question as a duplicate.)
The answer was sort of borderline, on the issue of whether or not flagging was appropriate. When people link to another answer that is also on Ask Ubuntu, and what the answer says is exactly the same method, with no differences or additional explanation, and the question is actually a duplicate... then the answer is effectively a "Possible duplicate" comment, even if it quotes from the answer it cites, and it doesn't really need to exist as an answer.
So I would be willing to flag such a post as "Not An Answer." I would not recommend flagging it as "Very Low Quality." The VLQ flag is only really considered correct in a small number of cases. On answers this is essentially limited to the situation when the post makes no sense and can't be edited to make it make sense.
The "Disputed" Status
A post that isn't deleted through review doesn't have any special "disputed" status (though there is a record of the review in the post's timeline). It's just a post that hasn't been deleted.
The status of "disputed" applies to flags, not to posts. A disputed flag is a flag that other users disagreed with, such that the result of the disagreement was for the flag not to be actioned. Flags where there is disagreement but they lead to the post being deleted are still marked "helpful."
We say that, the more "helpful" flags you have cast, the better, and the more "declined" flags you have cast, the worse. Similarly, it is neither good nor bad to have cast more or fewer "disputed" flags. If your concern is that you may have caused someone to have a flag marked "disputed," don't worry, because that's not actually a problem.
(Back when the system displayed "flag weight" to users, weight was increased by each helpful flag, decreased by each declined flag, and unchanged by each disputed flag.)