Answer:
Situational irony.
Step-by-step explanation:
Situational irony is a literary device used when the author wants the readers to expect something but ends with the opposite. Here, the author uses Scout's situation to derive the irony in the passage.
Scout who had a bad day at work stumbled across a movie set while returning home in a deep thought. The author used that situation to derive the irony by making Scout jump into the movie scene trying to help the actor who was in distress. Ironically, it was all a scene in the movie and Scout wasn't aware of it.
The author also used humor by mentioning that the shoplifter outran Scout. This is because Scout was a security guard and it was his duty to apprehend the shoplifter but he couldn't do that too.