Answer: Nobody said they know it was a companion. We're just guessing. And having been through the all 8 class storylines twice now along with all the other missions, my best guess was Risha.
Retraction: However, after searching my memory banks, I have recalled the correct answer. And no, that doesn't mean I searched it. I remember it now.
Answer: The one who said it was Kalyo.
Statement: It stuck in my mind, though the reason is silly, because she mentions backstabbing, and that's what the Operative's skill is, Back-stab.
The issue is that being Risha wouldn't make any sense to begin with, seeing that you only get her AFTER
chapter one. By "nobles", I guess we're talking about Alderaan.
Also, can't honestly remember Kaliyo ever uttering this line but I guess I can always check it later and I've done the IA storyline four times by now, having repeated each class story three times at least, except for the Trooper and BH.
Still, like I mentioned, I might have missed it.