You guys know islands don't actually have a specific definition limiting their size, right? Australia is wider than the moon. Visual media generally isn't entirely accurate on account of the fact the creators don't check for scale and if they did it may interfere with the visuals. We chose what I understand to be an arbitrary size because it changes across parts of the cutscene (almost as if they didn't plan on it having a set size so much as they intended for it to be the moon).
The Moon moves about 15 degrees an hour across the sky and I think we see it in
orbit along with the earth for about 4 seconds. 4 seconds is a 15th of a minute and a minute is a 60th of an hour. So in 1/900 of the time it takes to move 15 degrees it would move about about 0.0166... degrees. As our moon appears to be 0.5 degrees in diameter compared to the sky we would see it move less than 1/25 of its diameter and the moon in the cutscene probably is a few degrees larger.
It didn't return to it original position as it wasn't directly above the island when it when back up and it fell straight down when it hit the island.