On the other hand, 1080p clip was first compressed server-side, then scaled on your machine. In this case the 720p video was first scaled, then compressed. Let's assume that original video was 1080p. It won't be exactly the same, though, because compression and scaling are applied in different order. 1080p video would have to be downscaled anyway.
Differences in video probably won't be noticeable for untrained eye.
