Two trains of thought on this right now:
1.) The "Earth" we saw wasn't our Earth, and they will discover a planet, and call it Earth, and that will be our Earth
2.) The "Earth' we saw was our planet, and we are thousands of years in the future
Except you are forgetting that when they first showed "Earth", we saw the landmasses, and they were exactly as they are on our Earth. You could easily make out North America, for example. So it has to be 2.