What would cause it to pop after all this time?
Usually, this happens when a user flagged that post as Not An Answer. Both the Very Low Quality and Not An Answer flags put an answer in the Low Quality Posts review queue (if it didn't have one before) and the Very Low Quality flag is not available on posts older than 7 days.
Another possibility would be that this is a review audit but they're not enabled on Webmasters Stack Exchange.
This might be a real bug in the system, or not; anyway, I now remember I asked about a similar case a couple of months ago on Meta Stack Exchange: Answer in Low Quality Posts review queue without flag but no response so far.