[archmagi]

Just checked the book. This is in the "betting at the end" section, and I think we're only supposed to analyse the action at the river [img]/images/graemlins/confused.gif[/img]
I think the point is to be prepared for anything when you don't raise the flop. It seems they are reading a possible two-pair at BB and are worried about a straight at the button.
The next question is, what do you do if the button raises after you check at the river after just calling at the turn, hence have shown weakness.
Going back, I think I would bet the turn, and if I can't drive out anybody check the river.