I can't speak for all different hand grenades, but the sort I've seen have a separate detonator tube. The grenades are stored without detonators for reasons of safety. Throw it as far as you want without the detonator, it won't work. When you prepare it for use the top of the grenade is unscrewed, the tube is attached and then it all is put back together. Ready to explode!

Someone unfamiliar with the grenade type could just have failed to make it operational.