For what I knew, a post in the Low Quality queue stays there until one of these conditions is met:
- 6 "recommend deletion"
- 3 "delete"
- 3 "looks ok"
This seems to be covered by this Meta post from when the LQ review process was changed. The process depends on numbers of flags and can send posts to a mod queue, so a mod would have to let us know for sure what happened.
This part seems to be key:
ReviewsRequired = 1
Effective # of reviews required == ReviewsRequired + # of applicable flags
Task accumulates EffectiveReviewsRequired "Looks Good" reviews.
Outcome: if the number of (Recommend)Delete reviews is >= the number of Looks Good reviews, mark flags "disputed" and raise DisputedLowQuality mod flag. Otherwise, mark flags "declined".
So it seems that with 1 flag, a post would only need two "Looks Good" reviews which matches your second two examples. Since the "Delete" reviews outnumbered the "Looks Good" maybe they went to the mod queue and that counts as "review complete" as far as the LQ queue is concerned. If that's true then the mods evidently decided they weren't so bad as to need deletion.
On SO the ReviewsRequired is 2, so with one flag that may be the requirement of 3 that you are thinking of.
For your first two examples, I would guess that those posts were automatically added to the queue by the quality system. Those would not have any flags, meaning that the EffectiveReviewsRequired is only 1.
Also note that the deletion votes take into account post score and reviewer rep.
Three delete votes from users >=20k rep, and a <=0 score will get a post deleted.
Six Recommend Delete and Delete votes will delete a post with <=0 score, but posts with positive score go to the mod queue.