If your knees hurt, you start walking in an awkward way to protect them, which eventually causes your feet and your hips to hurt too… Especially if you are carrying an unusually heavy load.
Imre and Peter decided to stay at the camp closest to the summit (Sheep Camp) for another night. They needed to recover before attempting the next section, which is the hardest part of the trail. This section can only be accomplished in its entirety, as there is no other camp site until after the summit. They realized they had to rest in order to have a chance of making it to Happy Camp the following day.
They walked around just a little bit, to explore the area and fill up their water containers.