I'm not the moderator that handled your flag, but here are my thoughts on this:
Generally, I'm of the view that we (moderators) leave the Not An Answer (NAA) and Very Low Quality (VLQ) flags to be handled via the review queues for a decent length of time, unless the post is obviously NAA or VLQ. Where we do take action, we should expect to defend the decision (here on meta) if asked.
That does not mean that we don't also work the review queues (where any mod action is instantly binding), just that we don't handle the flag that caused the post to enter the queue right away. In fact, NAA and VLQ flags aren't even visible on the moderator dashboard by default for the first 15 minutes.
My reasoning is that users who have not yet earned the 20k trusted user privilege need a way to propose deletion of an answer without requiring a moderator. In most cases, this works well, and the users working the Low Quality Posts queue handle the flag by completing the review process. In this particular case, six users eventually voted to delete the post (with one dissention), though it did take 14 hours to get to that point.
Meanwhile, the active VLQ flags show on the moderator dashboard, and nag at us. We do try to leave these for a reasonable time, but it is not unusual for a moderator to step in if the process is taking longer than we would like. Note that handling the flag (as a moderator did) does not dequeue the post from Low Quality Posts - the moderator would also need to process the review queue item explicitly ("Looks Ok").
The general flag handling options available to the moderator in this case are:
- No action (leave it to the review queue).
- Mark as helpful, but take no other action (review process continues).
- Mark as helpful and delete the post (review process completed).
- Decline the flag (review process continues).
- Decline the flag and end the review with Looks Ok.
This is a judgement call that I will leave to the handling moderator to address in detail. If I were forced into expressing an opinion, I think I would choose from the first three options, since flagging to put the post into review was 'helpful' to the site. I will also say that the situation would not have arisen if more >= 2k users had processed Low Quality Posts in those 14 hours.
Finally, I'd say it is helpful to downvote posts you feel are VLQ because 20k users need an answer to be negatively scored in order to vote to delete directly.
Related on meta.SE: Is the Very Low Quality flag too ambiguous?