It is a logic puzzle, so 'lie' means saying the exact opposite of the truth. The clues they give are below, from the walkthrough. You can mindread Keara or find a note (near the first statue IIRC) to learn that they lie.
For a moment I did think of doing the opposite but I read Keara's mind and picked up the note. The thing is, the note vanished as soon as I picked it up. It was neither in my inventory or at the battle tower. I just followed the spoilers, otherwise I'd have to spend the whole night trying to find the right combination, thanks.
