This is just a theory, so FWIW...
Depending on how you view threads it changes the order they are displayed...I think linear is just by date/time...but if you view in threaded or hybrid they are in "conversational order" or whatever the proper term is. So if someone quoted a post a few days before, it would show it after the post that was quoted if that makes sense.
Again, just a guess without investigating it, which I probably should do before opening my big mouth but hey, what's life without taking chances? :lol: