Beleriphon
Totally Awesome Pirate Brain
I can buy that reading. Seeing the next few pages should make it pretty clear.
It think it goes both ways on that one. The setback is the same as a deadly to different leveled groups. Essentially if the trap is a setback to a high level group then it is by default going to be absolutely deadly to a low level one. That isn't much different than monsters really, an adult white dragon is at best a setback for a twentieth level group, but its a guaranteed TPK for a group at first level.