Does that mean it can’t be found on the original thread anymore?

No, it just means that it floats to the top rather than being a child of its original parent. If you're not seeing it, that's probably because the thread is paginated and you need to click "More" at the bottom of the page.

I wrote recently about the different reasons why we do this, if anyone's interested: https://news.ycombinator.com/item?id=27132402.