Seems like a child comment has been detached from this thread and moved into a separate top-level thread, that is currently at the top (https://news.ycombinator.com/item?id=23223772), while its' former parent (comment that I'm currently responding to) has been moved to the bottom (2nd page). QED.
If we're downweighting an off-topic subthread A, but it has a subthread B which is actually on-topic, we sometimes detach B so that it doesn't get pulled down by its parent. This is a good example. In this case A and B were almost completely unrelated.
