If you read Howard’s book or Edkins book or the magazine articles Hill wrote, after killing the elephant with a lung shot Howard Hill tried a brain shot on the dead elephant. That’s what the hole is. Howard found out a brain shot with an arrow was not a good idea.
There have been many misinformed that think it is a bullet hole, if you zoom in on a larger clear photo you can actually see the slits from the broadhead blades.
Howard killed 4 elephants however one was finished with a rifle and was not counted as a bow kill.