Farm's animals are more or less tame. They don't fear much the humans. This could explain why the Oryx let the poor guy get this close and then kill him.
I guess it happened in a Photosafari or Vision farm. In a hunting area, usually the game is more circonspect and this Oryx would have scramed long before the guy would have seen it.
Could this stupid death be a lesson. But usually protectionnists are ...................................deaf.