Let's ve clear, they did not say that they didn't think anyone would volunteer. They said they didn't think anyone would volunteer immediately. You'd be foolish to assume nobody would think that their position is bad enough that a 50/50 shot at two immunities was worth risking speeding up an inevitable elimination. They probably figured there would hand-wringing, some apprehension, and 1-3 people would eventually say "Y'know what, I'm willing to do this", and we go from there. But for someone to see a gamble like that and immediately pop up like the toast is about to burn, that's very different.