volgens Colin Fraser.
This is the date of the version release:
<MOODLE_VERSION>2007021534</MOODLE_VERSION>
<BACKUP_RELEASE>1.8+</BACKUP_RELEASE>
So you are spot on when you are suggesting it is a v1.8 file. There have been a lot of changes to the database since the release of that version.
What you might want to try is to change the name of the file to a *.zip, then it might handle it completely differently. I have had success at restoring zip files from a v1.9.4, but nothing earlier I am afraid. I think though it was only the course materials I got, but I really did not want the student details anyway. Good luck..