How To Train With a T. Rex: pages 16-17
The whole eating up to 10,000 calories thing is fascinating to kids, so it was fun to visualize the fact that it would be like eating tons of pizza. Of course, eating just pizza would be sorta not healthy, so that's why you see a "I could never eat that much pizza!" line.
Easter Egg alert: the name of the pizza delivery service is "Ava's Pizza".