How to Model Almost Anything - Exercise 2

I am getting ready to use the curriculum in my class and have been testing the exercises. As you go through Exercise 2 you work on "Cool Bike" and then it shifts to "Cool Car" for a page or 2 and then right back to "Cool Bike"

Is this an error or are you supposed to bounce back and forth? It was confusing to me and I can only imagine what my students will think when they get there.