The question's timeline shows that it was re-opened on 2023-11-04 at 23:14:10Z, answered at 23:15:25Z, and re-closed with the same duplicate target at 23:18:17Z by the same user -- a span of just over 4 minutes. No other events are recorded on the timeline between the re-opening and closing. It may be permissible in rare cases for a user to do this (e.g., if the user is only made aware of new information that convinces him the question should be closed after he has re-opened it and posted an answer, or to change the close reason), but this is not one of them. No new information was made available between the re-opening and closing, so this user clearly knew the question should be closed at the time of re-opening.
The purpose of the re-open privilege is to re-open questions that should not be closed; the act of re-opening a question that one knows should be closed is contrary to the purpose of the re-open privilege so it is an abuse of that privilege. In this case, the user who abused this privilege had earned a gold badge in story-identification and was therefore entrusted by the system to unilaterally re-open and close such a question for the duplicate close reason -- this is a further abuse of the re-open privilege and the trust given to this user. The user also benefitted from this abuse of the re-open privilege and trust by posting an answer in order to gain reputation1 from upvotes and answer acceptance, which further compounds the abuse of the re-open privilege.
It has been argued that the help center does not explicitly say users are not permitted to re-open a question just to answer it and close it. This is because the help center is not designed to explicitly state every obvious fact about the network. Nonetheless, there are several not-so-subtle clues that this behavior is not permitted. For example:
- The help center article on the reopen review queue instructs users to "evaluate the question as it is now" and "leave [it] closed if any close reason(s) still apply". Since the question did not change nor was the re-opening user made aware of any new information, the correct choice is clearly to leave it closed. The same instructions apply both within and outside of the actual review queue -- another fact that is not explicitly stated but obvious.
- The system does not allow new answers to be posted on closed questions. The fact that the user needed to circumvent the system's rules is an unmistakable sign that such a question should not be re-opened simply to answer it and re-close it.
It has also been argued that duplicate questions may somehow benefit from posting duplicate answer(s) on them. That may be the reader's personal opinion, but it is not the well-established philosophy of the Stack Exchange system -- which is that duplicate questions should be closed and linked to the original question so that, ideally, all answers are posted on one, canonical question. This avoids the need to post duplicate answers and reduces the likelihood that users will need to browse to all the duplicate questions in search for a sufficiently good answer.
The duplicate answer posted in abuse of the re-open privilege is not obviously better than the answer to the original question, and contravenes the Stack Exchange philosophy on duplicate questions. Therefore, I have deleted it. The user is free to post an answer with any additional details on the original question.
1In the form of useless Stack Exchange Internet points, but likely not in the usual sense of the word.