My understanding is that Matt did not import his images from his Menalto Gallery install into WP. If you check out his site, his WordPress galleries only go back to November 2007 and I know that he had many more (thousands?) of photos prior to that. As far as I can tell, his Menalto Gallery images are no longer accessible from his site.
Regarding Matt's comments on this, I remember him saying something about this when the new WP gallery feature was first introduced. However, I believe that he was referring to the fact that he had simply added many photos into WP and not that he had imported them into WP from his Menalto Gallery.
I've been searching for a script that can import my Gallery2 library into WP, but unfortunately have come up empty. As such, I am continuing to use Gallery2 instead of the WP gallery feature.