presumably someone else posted something on another thread and that has gone to the top of the list (as this one will in a minute). All you can do is try to remember what it was, or go into naomi's profile and look at the list of threads she's posted on recently.
They dont disappear from AB they just drop off the list of teh 6 latest posts. You can find a recent question by clicking one of the tabs- something like Recent Posts or Recently Answered