NormanS is 100% right. At normal speed, it looks odd, but slowed down, it's very obvious. The camera is definitely panning--the death star moves out of the frame, and there is a shift in the star field, but the explosion sticks right in the middle of the screen. Smack dab center, no doubt about it. It's not a biggie, all things considered, but it might be something Adywan will want to take a look at, because it'll definitely catch the eye of some folks.
To look a little more realistic, it would have to shrink quickly in order to give the sense of forward motion, away from the viewer, and move a little up and to the right, I think.