Quote: "Is it a movie they're pasting sprites onto?"
I know you can't put sprites over a video in AGK. So that wouldn't be the way to do it with AGK.
My guess is it is an animation, straight up. With other things displayed over it. Simple animations are doable in AGK.
Or, it could be a single image for the background and a somewhat transparent image being rotated about.
How they are actually doing it in the app you point to, no idea.
It just matters how you want to do it.
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master