Though Harry offers little insight into his third-year History of Magic curriculum, it presumably deals with historical witch hunts: Harry spends much of his time in Diagon Alley writing his summer homework essays on witch hunts, and his final exams also ask about the subject. When the novel introduces the reader to Harry doing his summer homework on witch hunts, it sets the stage for the novel's deeper exploration of the wizarding justice system. In this way, the historical witch hunts that Harry learns about in school--which were, per his textbook, ineffective, silly, and misguided--set up the precedent that so-called justice isn't always just. However, it's also telling that the historical witch hunts were conducted by muggles using their own justice system. In this way, the novel also illustrates how much perspective matters: while the muggles thought their hunts were good, just, and effective, the wizards knew that the hunts were none of those things.
Witch Hunts Quotes in Harry Potter and the Prisoner of Azkaban
Non-magic people (more commonly known as Muggles) were particularly afraid of magic in medieval times, but not very good at recognizing it. On the rare occasion that they did catch a real witch or wizard, burning had no effect whatsoever.