I don't get it, I thought humans discovered flood in halo 1. Maybe you play as the covenant against them. And as Cliff said below me, I couldn't think the flood could look as repulsive as in Cortana.
EEEEWWWWWWWW! I absolutely hate the flood. Its so freakin scary. Although you can't beat playing H2 and H3 against them in campain. Specially when its night and somebody is sleeping over and playing it with you. This looks cool but I am more interested in H3 recon. The whole "Chess" stratagy thing doesn't appeal to me and I would rather play customs on forged maps, owning campain with your friends or playing as a team with your buddies from school. This looks cool but H3 recon looks cooler. Nice find though I believe you were one of the first people to see this.
I have a theory that the Spirit of Fire was destroyed with her crew at the end of Halo Wars. If you want to read the whole thing it is here.