Canister Bomb physical damage?

The ‘Concussive Bomb’ add to Canister bomb states that 100% physical damage can be transmuted to lightning damage. however canister bomb itself only does piercing damage. Does this imply that the piercing on Canister bomb is physical or is this some kind of error in the tooltip?

look on 2nd node
trauma is the DoT of phys dmg, so it becomes electrocute
(would also mean if you were to obtain any flat phys mods to canister it would have been converted to lightning - but in this case it’s for the Casing node)