Yeah. Because really, only Xykon (of known NPC's) is powerful enough to kill that many people before they can even react.
If it is an illusion, then the question becomes, what is Drake trying to accomplish? How does this throw would be gate finders off the scent? You could do this with a treasure that was mobile, the whole, "Some one has already come and taken what you were looking for!", shtick, but it doesn't really work with the gate. I suppose you could be trying to lure foes into a false sense of confidence, but right now I'd be thinking, "Oh crap, something is here that killed off an Epic level illusionist's family. We need to be extra careful now!" If you were going the 'false sense of confidence' route, you'd have an illusion of skeletons, not recent corpses.
So, right now I think we have to operate under the assumption 'Xykon was here.'