I don't know anything about the leaks, but I think you're right and the blue robot/narrator is a companion. Or at least, the NPC we meet that starts the questline. She seems cool, very classic sci-fi assistant robot kind of voice - and I think we can fully customize her into any robot, not just a blue Assaultron, even customize her voice.
The robot jumping and stabbing I think was using an Assaultron killcam that already exists in the game. I'm surprised at how well the animations look - I was sure that the biggest hurdle to making robot hybrids was getting them to animate properly, but it actually looks pretty good, like they can just associate animations with the different limbs and it all blends fine.