I was actually investigating damage types recently because I had the same thought. The Forgotten Realm wiki actually says that smoke powder IS a magical substance (
https://forgottenrealms.fandom.com/wiki/Smokepowder).
"Bearing a resemblance to gunpowder, it was a coarse dark gray powder that exploded when exposed to fire or heat, producing force, noise, and smoke. However, smokepowder differed by being magical in nature."
I know in Waterdeep: Dragon Heist it deals fire damage, but I think force damage is a fine alternative as it's suppose to be an "explosive" substance (magical gunpowder).
I do have a problem with a lot of resistances though (specifically in grymforge), where a lot of walls / obstruction has vulnerability to force but not bludgeoning (I don't see a reason why, aside for Larian to force us to do it "their" way). Even the deep rothe wildshape does force damage outside of combat for some reason.
Also, why the hell do the goblins have these bombs if it's such a rare substance (nothing is more tilting than getting randomly bombed by some goblin for 20 damage each out of no where. I pray larian fixes some of the enemies item lists).
