DVDs use the MPEG-2 video codec
correct.
and have a file size of 9 GB typically
Incorrect.
Though there exist dual layer or DVD9 commercial releases they were usually either double features like 2 movies on a disk or 4 TV episodes or uncommonly long films (Lord of the Rings for example).
MOST commercially released DVDs were DVD5 or about 4.7GB in size. And this is based on oh 20 years of sample size.
On DVD encoding: Things get tricky in comparisons because AVC introduced a lot of tricks to get lower bitrates while maintaining a certain psycho-visual level of passing image quality that MPEG2/4 simply didn't have. It may not pass detailed frame by frame study of corner elements but for most people without perceptible quality loss you can knock the bitrate down meaningfully beyond the pure compression efficiency improvements of the follow-on codecs.
Perhaps contained evidence against the former PM who tried to do a military coup and this is the way of getting rid of it? Perhaps protecting co-conspirators if not the top guy.