After thinking to it, I wanted to give my idea about the question.
For your main question: Should questions “solved by a reboot” be closed
It's a case by case for me. As like the example you gave, yes. The fact you talked of it there on meta accelerated the closure without any more intervention from you. On the other hand for a router or a switch, that a reboot resolve the issue, it can be a firmware problem or such that the trouble can come back later when the gear is in overuse, so it can be tricky to close all such question at first sigh. I v-t-c on the example you gave, but I would not v-t-c on all issue that a reboot might solve the issue.
For the second part of your question, how the moderator's reacted;
How does this require mod intervention. Write a self-answer or delete.
I feel like RobMoir's told, as I just think the moderator though you were the OP.
I searched through meta stackexchange, and the usage of custom flag is not directly stated when to do or not, as comment like that seem constant;
Well, as I see it custom moderator flags shouldn't be used to just
close a question, except in extreme cases e.g. bounty preventing
standard close votes, user who post tons of crappy questions, etc.
or there is a point of view that I like for using close flag (not custom close flag) wrote by womble;
When you flag a question for mod attention, you are requesting
closure. As Michael Hampton described, it turned up in the close
review queue and, as I believed the question wasn't worthy of closure,
I clicked "Leave Open". A mod clicking "Leave Open" is not some sort
of super-vote that causes the question to be forever left open. All it
does is clear the flag (if I had skipped the review, another mod would
still have had to deal with it).
As you can see using a moderator flag can be tricky if the moderator don't think like you as from him a leave open vote will decline your flag, but keep in mind the intent is not to rebuke yourself. The intent is just that if the moderator don't think at 100% that it must be a direct closure, he will then wait the community to close the question.
Ofcourse, when you will be at 3K, this discussion will be history :)