Hive Knights do not count for any type of kill towards bounties whether it's grenade kills, precision kills, majors, ability, or weapon. Also kills with grenade splash damage does not count either and not the bounty was not for attachable grenade kills. Titan lightning grenade just disappears if thrown and it hits multiple enemies before it touches the ground. Also, what's the point of buying legendary cryptograms from the cryptarch if he doesn't give you one near your light level?