A lot of demo effects are almost like magic tricks --- before you understand how they're done, they seem like impossible magic; but once you do, you think "that's so simple, why didn't I think of that?"
Animation by essentially "panning" inside a larger pre-rendered image is one of those tricks:
Old-school demos have another common trait with magic. Like the best stage magic, you know you are being fooled - but even after seeing how the trick is done, you remain amazed by it.
