Notably, these kinds of scenes aren't there to sell the audience a false bill of goods. Quite the opposite, in fact: the first few chapters of a story aren't always representative of the whole, hence the addition of a prologue to give the audience a sense of what's to come in later chapters.
As an example of what can happen when an author doesn't do this, Dan Wells' I Am Not A Serial Killer is about a teenager who works in a mortuary and investigates a series of brutal deaths around his town, and discovers that the killer is actually a millennia-old monster. The supernatural reveal doesn't happen until halfway through the book, and if you go on Amazon and sort by 1-star reviews, you'll find a lot of them come from people who thought they were reading a crime story and then got upset when they discovered they were reading a paranormal YA novel. When it came time to publish Wells' next book, his publisher told him, "This time, we're putting the monster on the cover of the book."