The throw looked quite good to me, on target and flat enough, no idea if the force would have been sufficient to penetrate enough, but the "samburu" spears are effective due to their design. He is right in the buffalo raised its head and the spear was deflected by the horn. First handgun shot dropped the young buffalo too, so may have been a brain shot (?).

Edited: I see Matt has posted the same time as me, as I hadn't seen his post until after my post was posted. My post was 100% independent of Matt's