As for that "world first" claim, there should be an asterisk *Dreadguards was mathematically impossible at the time*
Except it wasn't mathematically impossible. At least 3 guilds cleared NiM DG in under 5 days.
Yogg-Saron "Alone in the Darkness" took about 40 days.
25 man Heroic LK took weeks as well.
I think DiLiH said they needed 150-160 attempts to clear NiM DG. While the 2nd boss in a 5 man Operation being that much more challenging than the other bosses was probably unintended (hence the 30 second enrage nerf) it was hardly impossible to beat pre-nerf.