I think those are two different rooms. I think Orolin was alone- that's why the trolls couldn't find him and no one knew he had died.
Wasn't that particular chamber also only accessed by preservers? And the trolls had been trying to open it a long time and Timmain said there's no way to without a preserver.
I guess this might be dumb question but I'll ask it anyway: Are all the rooms in the Palace fully explored? I am pretty sure Timmain knows the Palace inside and out, but I've always wondered if there are hidden chambers that even she doesn't know about. Not likely, but the thought of it is kind of interesting.