None of the events in Destiny actually happen in Destiny's universe. It's all a simulation by the Vex to determine our strengths and weaknesses. That's why you die whenever you try to leave the battlefield. That's the Vex making sure you don't stray too far outside the boundaries of their simulation. This is why we fight the exact same enemies and kill the same bosses over and over again. It's all just different simulations run by the Vex to see what kinds of strategies we can come up with. Remember the opening cutscenes for the game with the astronauts on Mars? Watch the mountains as they walk. The mountains seem to jump around. Can you guess why? Different simulations by the Vex. Oh, and the Exo Stranger is capable of hacking into these simulations and uploading her own persona for short periods of time. That's why she doesn't have time to explain why she doesn't have time to explain. It's also why she has such a strong hatred for the Vex. Nothing is real in the game's universe. It's all a bunch of programs created and run by the Vex.