That photo is in the Osprey on the Great War in East Africa, but there is no info on it bar the caption, which suggests that picture is possibly pre-war and that the original caption referred to the contraption as a 'bomb-thrower.' It suggests they had these things on the inventory for fighting (or frightening) native opponents and that they still had a bunch of them kicking around at the start of the war.
Sorry, that's all I got.