It'll be based around loot tables and percentage drops, by having people submit what they got you can maybe see if things have a higher percentage. Hard to say if it works like DIII, but that is RNG as well, but operates on a Loot Table, in that everytime you start a new game you have a different loot table that the RNG draws from....so if you have something good drop, you can usually go Kadala and buy the item type and you sometimes get the same good item. Your rewards are random, but they would have to be drawn from some sort of pool or table of items that changes everytime you load a new game, which is why you dont get the same thing everytime.