How does additional damage work with the Hand Mortar’s explosive property?

So I am building a gunslinger, and see a possible very high risk, but very high reward tactic for large groups.

Say I have a hand mortar, and fire it into a creature surrounded by at least 2 others. The hand mortar has the explosive property

Explosive. Upon a hit, everything within 5 ft of the target must make a Dexterity saving throw (DC equal to 8 + your proficiency bonus + your Dexterity modifier) or suffer 1d8 fire damage. If the weapon misses, the ammunition fails to detonate, or bounces away harmlessly before doing so.

Now say I choose to spend 2 grit points on the Violent Shot trick shot.

When you make a firearm attack against a creature, you can expend one or more grit points to enhance the volatility of the attack. For each grit point expended, the attack gains a +2 to the firearm’s misfire score. If the attack hits, you can roll one additional weapon damage die per grit point spent when determining the damage.

Does this mean that if I hit and do not misfire (roll above a 7, and above the main target’s AC) I deal 6d8 + DEX fire damage to the main target AND a potential 3d8 fire damage to the creature around the target, or does the "splash damage" not count as weapon damage?

This is entirely based on the DnD beyond Gunslinger subclass definition.