yes they are both correct
If there was a post that has not had any new postings for XX hours/days it will move down the list of threads accordingly. If it was important, one might post saying "bump" so it goes to the top of the list for others to see.
Another scenario would be that someone posted a question, but never got a resolution. Instead of posting another question of similar nature, they just post BUMP to bring their question back into circulation.