Sometimes the time of the last post to a thread is displayed wrong in the list of threads in that forum. E.g.
this thread - at the moment in the list it says the last post was 11-12-2002 03:18 PM
by wulf, whereas when you look at the thread, the post was actually 3:08 PM.
I've seen this happen a couple of times, the thread gets bumped up when no-one made a post, and it thinks there was a post later than there actually was one.