No, it isn't, it is true 1080p. When they did the scan for the 2004 DVD, they made it @ 1080p. Here are some comparisons someone made ages ago:
http://www.pauliesworld.org/swhighdef/sw4_1.html
http://www.pauliesworld.org/swhighdef/sw4_2.html
There would be no reason for me or Adywan to do our edits in HD, if the source was just an upscale.