Actually I just remembered something when Yun used the painting of the the painting in the fire nation poetry hall to escape it was stated that the pigment of the paintings exploded on impact and I remembered that long ago pigment was actually used to create guernades back in the so this means Yun essentially lunched grenade bullets in this scene what do you think about it?
Maybe that was where the inspiration from that came from but I don't really think that you can fully equate the two.
I don't feel like doing research right now so i'm just going to trust you on this but I would think that there are still differences between pigment used for weapons and for fine arts. Also I am uncertain if he would be able to create as much force but that is maybe possible, at least when compared to relatively old grenades.
Additionally it would probably still lack the heat grenades carry as well as metal most likely still being stronger than compressed paint?