This type of situation can happen many times in games. There are two ways for using nades: either using the scroll wheel on your mouse to select it, then by clicking or holding the left click, or by simply clicking or holding right click to throw the nade except if you are using sniper.
One of the ways this can happen is that right before they die they press their right mouse click and drop it, or they could have been cooking the nade while you were killing him which always concludes with the nade being dropped. So always make sure that if you hear a grenade sound after you kill an enemy, make sure that nade isn't coming from the enemy you just killed!
HTH.
One of the ways this can happen is that right before they die they press their right mouse click and drop it, or they could have been cooking the nade while you were killing him which always concludes with the nade being dropped. So always make sure that if you hear a grenade sound after you kill an enemy, make sure that nade isn't coming from the enemy you just killed!
HTH.