It must take quite a feat of balance to successfully maintain this pose, and to get up to, and down from it too. It would be all to easy for him to overbalance and, failing to grasp the pole again, then crash to the ground, but they never seem to do that.
Another wonder of evolution - chimps are descended from apes who didn't fall out of their trees (or at least didn't fall too badly until after they had sired/raised at least one infant)