Actually five targets went down in this room. The two near the door were guards. The one closest to the hole Damien opened had been sitting near the tube that would activate the "bots" trap in the outermost corridor. The three figures who'd been arguing were not dressed as guards, but were instead dressed in high quality, functional clothing, not overly elaborate but fancier than a commoner could afford, and one of them was wearing leather armor.

It's not clear what the distinction between the three unknown characters and the guards actually is, since you didn't have a lot of time to observe them. The guards are decked in enchanted mail, coveted over by thick, coarse, voluminous robes with heavy hoods.