The distance to the earth might have been coincidentally the same as the distance to the other satellite. LEO isn't that far up, the one that took the photo was only ~600km AGL.
Edit: you're probably right, actually.. the silver square on the lower section of landsat 8 is ~1.5m high (guessing from the image on wikipedia), so there should only be ~5-6 pixels for it, but there are clearly more.