I'm inclined to say much or all of the background is indeed all rear-projected. If you look at the top-right around 5:06 or 5:07, you see what looks a lot like it might be light-emitting text floating in midair. (EDIT: Correction! It's not just floating there, it scrolls left just as the camera is coming down, I missed that on the first viewing. So it's definitely not just on a physical banner.)

As for "massive resolution", slicing up a framebuffer and shooting out the components to multiple projectors wouldn't be a new idea, and I'll bet that's what was done here.