How did downvotes suddenly put these old answers into the Low Quality queue?

Question

This answer and this answer (both are now-deleted "looks good" answers with no detail), posted some years ago, were recently put into the Low Quality queue after receiving downvotes.

According to the queue, they were added because of their (lack of) length and content. When the system detects this, Community ♦ automatically raises a VLQ auto-flag that puts the answer in the queue. However, no flags were raised today or the moment they were posted.

Since they were never auto-flagged originally, is this a bug, or is this part of the system change that now puts Not-An-Answer flags into the Low Quality queue? If the auto-flagging system was around three years ago, then surely it would've caught them already.

Answer 1

There are three ways an answer gets into the Low Quality review queue:

1. Flagged by a user
2. Flagged by the system based on various quality checks run when the answer is posted
3. Directly added by the system based on a combination of the checks in #2 and various other criteria... Including the post's score.

The quality checks used for #3 are pretty weak; there are a lot of false positives. So if the post gets upvoted, it'll silently drop out of the queue. Or, in the case of very old answers like these that predate the review queues, it'll never even enter review.

...until enough downvotes make it eligible again. Which is what happened here.