The Exotic perk made me think of the jet pack wearing brother in Shield Brothers... Maybe from there? Also, the armor looks a bit like Cabal armor. The color is also similar to the mortar wearing brother. Maybe you need to kill that brother last in that mission? Every time I've played it, he's killed first, as he's the one charging you. Maybe it has a similar mechanic to the Psion Flayer claims, as the drop is dependent on which boss is killed last.