Basically, what this would be is that the hand grenade uses the same area in the hud sprites as the babblers did.
Each sprite for weapons, hud, stuff like that, contains a number of different images for different things. Basically so you can use 1 sprite to hold 20 images rather than 20 seperate sprite files. In the weapon_weaponname.txt and hud.txt (In your ns\sprites folder) it defines the sprite, starting corner (Top left) of an area in the sprite and the overall size of the area of sprite you wish to use. As i said before, the babblers image must've been where the hand grenade now is.
It seems you downloaded an old model which, for some reason, has an outdated sprite (hudw320.spr, and such) from one of the older versions and whoever released the model didn't think about updating it for 3.0.
Simple solution, find out the exact sprite name that the hand grenade uses (It will be in hud.txt) and get someone to send you the proper files.