Minecraft wiki entry for Death_messages, associated text: <player> was pummeled by <player/mob>
Is coded to appear when the player is killed by a snowball, egg or ender pearl shot by a player or mob. This is practically impossible, as these projectiles do not deal damage.
Blazes take damage from snowballs, which means that naming a blaze and killing it with snowballs will send this message to the game's log.
Because of MC-72151, a snow golem's snowballs are able to hurt and kill wolves, after which the message would appear to the owner of the tamed wolf.
Theoretically, when the player is killed by a snowball or egg shot from a dispenser or summoned with /summon, or an ender pearl summoned with /summon, the death message is <player> was pummeled by Snowball/Thrown Egg/Thrown Ender Pearl.
<player> was pummeled by <player/mob> using <item>
Is coded to appear when the player is killed by a snowball, egg or ender pearl shot by a player or mob that is holding a renamed item during the player's death. This is impossible, as these projectiles do not deal damage. However, as stated above, blazes take damage from snowballs, and snow golems can kill wolves, and if the killer in each case is holding a renamed item, this message appears instead.