You are right, but yes, you are slightly over-complicating. Or rather the Professor is.
In both cases there is just a gravitational force and no resistance/friction, so the whole thing (aka center off mass) drops down as far as possible.
For the ladder in the circle, there is however, an unstable equilibrium when the man is right in the middle, on top of the ladder. Also, without friction, he would rotate if he jumped on the ladder. But this should be explained in the book.
Aha, found it. He introduces potential energy with a simple example, because in the next one it is needed and it gets complicated. Nice book.