I believe the vex and the stranger are of course from the future but the vex actually are an evolved form of something we've come across one-too-many times in the story. Rasputin. Over time (decades maybe even centuries) the warmind built itself up and got...smarter. Not only did it evolve but the darkness made its way into the system. This main brain of the system which was transformed by the darkness became what we once knew as the Heart of the Black Garden. Just as Rasputin coarsed through most active defense systems on earth and the moon the mind of the Heart wirelessly controlled the machines that are merely counterparts to the main system.