Sikhs have no part to play in the caste system, period. It is believed that the gunman mistook Sikhs for Muslims and it has been suggested that this is why we went after them (after losing his marbles).
This removes, even further, the question of the caste system from this situation and if anyone takes up issue with gun control in the context of this shooting, the argument of getting that person's own house in order could be made on any other grounds, but definitely not one that concerns the caste system as far as I am concerned anyway.