Are a prologue and a preface the same thing? Or is there a distinction?
No they are not. See explanation.
A preface is not a part of the story, it is just a commentary to a book (often written by other person than the author of the book).
While a prologue is part of the story showing some events which happened before the main plot.
For example in "The Lord of the Rings" by John Ronald Reuel Tolkien there are both a preface and a prologue.
In the Preface Tolkien describes the process of writing a book. He also gives some directions on interpretation of different parts of the story.
While Prologue gves a description of hobbits and introduces the story of finding the One Ring by Bilbo (described in details in "Hobbit or There and Back Again")