You are correct, ISP has static routes for the customer subnets and a default route for upstream provider (provided they aren't  using BGP).

In the description just before the example it clearly states "The ISP router then has a static route pointing to the customer's network." which is the typical operation for ISP networks.

Even though the example is poorly written, I believe the point is to introduce the idea of a discard route. This is a practice used by ISP's to prevent routing loops by creating a "static default route" for the entire ip block used for customers to an interface such as null0.