"equivalent of throwing yourself atop a grenade..."
Wow! Thanks for your interpretation of the report - which really didn't make a load of sense to me until your post.
Sounds like perhaps they thought they could pin him..take him alive..for intelligence.keep him from detonating the bomb...or they didn't have a clear head shot....so possibly the leapt on him, pinned him, but when they couldn't see his hands..they fired intot he base of the skull...where the medulla is located..thus no chance of an involuntary "death" twitch triggering the detonator