I don't think "force damage" is necessarily something magical. It just means that things get pushed around when the powder/bomb expodes, like from real world gunpowder. From a real world bomb however you would expect piercing or bludgeoning damage from high velocity fragments though, but here they just choose to call it all "force damage". There may be a reason for that which become apparent later on when you find a use for the items beyond just blowing up enemies.
You're welcome to think that, but
officially Force damage is "pure magical energy focused into a damaging form."
Bombs, as Rag suggests, should do a mix of Thunder ("concussive burst of sound" = shockwave = like real world bombs/gunpowder), fire (fire), piercing (shrapnel), and/or bludgeoning (the shockwave could be given this "blunt force" damage, and large enough shrapnel could also deal bludgeoning).
I agree that bombs seem to have a too-high combination of damage and radius compared to other items. 4m = 13 feet radius is fairly large.
