I thought I post this since it is not included in the book, but IN Chapter 5: Camera, Page 129, it doesn’t mention in GameScene.swift to comment out debugDrawPlayableArea() in the didMove function and boundsCheckZombie() in Update function, before running the game! This will get rid of the red rectangle outline and let the zombie go past the first background image.
I am assuming you uncomment the boundsCheckZombie() after you update the code on page 135. The bounds code will allow the zombie to move in the x position without stopping at the end of the first background image. The zombie will still bounce off the top and bottom of the screen bounds.