nah, i bet it's that new joke green item "ogre slaying knife" which has the exact same look as the -50HP artifact you get from that ascalon quest, so it just looks like he's dual wielding, but infact it's just a joke sword and an offhand ...
either way, you could probably swap together a W/A and give it daggers and things. then you'd have what looks like a dual wielding wammo. only it's a "wa you're all noobs cause i have 2 swords"
he actually says "Im attacking the darkness" and if you hold ctrl while you attack The Darkness, it says "Im attacking The Darkness"
guild wars is great. i hope they release more joke items.