They were supposed to be.

by TTL Demag0gue , Within the shadow of the Traveler, Thursday, July 04, 2013, 07:04 (4179 days ago) @ Jabberwok

I don't really know how difficulty levels will be handled, if there are any, but those enemies seemed like a cake walk. I really hope the Fallen are tougher than that in the final game. Of all the enemy types, they seem the most similar to elites, but an elite would never drop from a single headshot unless it was from a sniper rifle. Maybe they dialed things down for the live demo?

They mentioned in interviews afterward that the difficulty settings were scaled way back for the purpose of the demo. I think Player 1 also had invincibility turned on. Staten mentioned that Rixis would have handed him his head under normal circumstances.