The pictures are in the gallery section of the site, put up by Adam. They were taken from an article on Halo.Bungie.Org about the "Combat 1" short.
I'm pretty sure Weta went full out with their work for the Halo shorts, so it's probably a metal/composite that they used. It might be a phenomenal paint job as well, but I think it's both.
It's technically possible, but without a means to either stamp or cast the armor it'd have to be cut and welded, and metal armor is generally heavier than fiberglass and resin. Although it can be thinner and still be structurally self supported, so that might even out in the long run.