I find your question unique and can honestly say that the subject is one that has never crossed my mind. After conducting some research, I can present you with the following information.
According to information obtained from the Library of Congress, coconuts are fibrous. Some fruits are a little more unusual than others and a coconut falls into the category of a dupe. If one looks at a coconut, one sees that the outside is covered similar to the seed of a peach. The crust of the coconut is hard and covers a single seed. When a person buys a coconut in a store, the coconut has been transformed from its original appearance.
Most coconuts have a green outside covering. The layer is called the exocarp. The next layer is the mesocarp and consists of a hard layer that resembles wood. The inside of the coconut is the endocarp. Coconuts that are sold in stores are usually stripped down to the endocarp. The endocarp is the part of a coconut that a consumer purchases in a store.
The inside of the seed is the part that is made into coconut chips or flakes. Because a coconut is a seed when it becomes fertilized, and conditions are right, the area where the coconut has three outside dots becomes the site for the plant to shoot through as the plant grows. The plant then grows into a tree.
However, the coconut does not demonstrate all of the characteristics of a nut. A true nut grows a plant after the outside of the nut breaks down and the inside releases. The truth is that a coconut fits three things and can be considered a nut, a tree, and fruit. Your question was great.