Are all enzymes proteins?
Until the late 1980's all enzymes* were believed to be proteins, and were often defined as protein catalysts, often in textbooks which are often not perfect representations of science. At that point every macromolecular biological catalyst known was a protein so they thought all macromolecular catalysts were proteins. But the discovery of ribozymes (RNA strands that act as catalysts) changed that. The discovery that one of the most well known enzymes ribosomes had their functional components made of RNA and not protein also played a factor. 

NOW enzymes are generally defined as macromolecular biological catalysts and include ribozymes. But older works or outdated textbooks will still refer to enzymes as only proteins but newer works will not. Don't feel despondent I was taught the same thing initially, and it persisted for a several years in college. Part of this is each successive step in education tends to lag behind and/or get over simplified in scientific knowledge. Textbook manufacturers are not overly concerned with poor phrasing or outdated definitions and are rarely writtten by scientists.   

*in its object form, originally and for quite a long time enzyme referred to the process not the agent responsible becasue the agent was unknown.