He ran like a house on fire is an example of an idiom, and more specifically a simile. A simile is a comparison between two unlike things. An idiom is a commonly used figure of speech.
Katniss does use simile from time to time.
Outside the window, a car comes to life, soft and quiet like the purr of a cat. (p. 30)
Authors use descriptive language to help the reader visualize something that may not be easily described. Sometimes this comparison evokes strong emotions. We can imagine someone running away from a house on fire would be frightened. Most of us know what the purr of a cat sounds like.