He shot thousands of Buff and Elephants. He brained the animal in that photo, he just waited too long and a dead elephant fell on him. There is a good video where he describes the pressure on PHs to wait until animals are around 5 yards away, though the law specified 10 yards, particularly when guiding photo groups.
His conclusion on stopping rifles was that you needed a double in the 500 Jeffrey class to achieve things the 9.3s and .375s could not. He did not think the 400s, 416s, or 458s were enough. His take is pretty nuanced, so he seems to contradict himself at times as he was around long enough to see poor ammo, and lots of different shooting in the mix.
He had fought in a ton of different Rhodesian wars, and also encountered poachers. One thing he struggled with was that he said you should have a rifle with 30 rounds should you have to engage criminals or terrorists. So as much fun as it is to shoot the heavies they don't do you much good if you happen on outlaws. Nor do most people, particularly in Africa, have the money to shoot them enough to keep proficient. So his 9.3 on a Demoulin action had a box magazine and an Aimpoint.