You chose which of the 3 weapon bounties after you got the initial bounty from "RNG" You then upon choosing that particular weapon bounty out of the 3. You then had specific tasks you had to complete before you had the usable Exotic weapon the completed bounty nets you. As opposed to opening a chest, completing a Nightfall, POE or Raid and having a chance of a shard, armor piece, shader, unnamed Exotic, Legendary or nada. Really, it's not that difficult to understand the difference.