Ask HN: How are posts being reparented?

I've noticed twice now, and commented once about it here with a picture of the post hierarchy before the reparenting happened: https://news.ycombinator.com/item?id=20246152 Here is the picture of the hierarchy before: https://i.postimg.cc/W1ytffL2/hn-post-moving.png And here is how it is now: https://news.ycombinator.com/item?id=20244726 Is it automatic, or done by mods, or is there an option to do that that I've missed or that is gained on reaching some karma threshold?