The question isn’t if there are multiple points of determination as to whether the target takes damage. A damage roll occurs after such determination. You have two separate sets of rules each instructing you to roll dice to determine an amount of damage to be dealt to a creature (i.e. a damage roll). That both sets of instructions tell you to roll the dice when you hit the creature with an attack is immaterial to the question of whether or not the damage rolls are the same, and I cannot fathom how you could interpret them as being the same. They are very literally two separate acts of rolling dice to determine damage, each dictated by separate rules parcels, and each assigning different damage types to the values determined by the rolling of the dice. In what world could they possibly be considered the same roll?