Subsequent to my posting this Meta question, the question I referenced in my post has been put on hold. I therefore conclude it was correct to initiate action to close this question.
Based on the following comment on the question, it appears a custom-close reason was used:
I'm voting to close this question as off-topic because a reboot solved the problem.
This is indeed what I would have done if I had the necessary rep.
It's still unclear to me if it was incorrect to use a mod flag in this case. As the question is now closed as "off-topic", perhaps I could have instead flagged it as such. However, I observe that none of the close reasons available to me1 reasonably describe why this question should have been closed. Had I flagged it as, say "Blatantly off-topic," I would expect close-voters in the queue to observe that the content of the question is in-fact on-topic, and disagree with the close flag.
It would still be helpful as I continue contributing to Server Fault to know what is expected of me in a case such as this.
1As of this writing I'm a 1.9k rep user and don't have access to the free-text close reason.
