How is fiction and non-fiction the same?

Fiction is based on imagination - not real. Nonfiction is based on reality - fact. ..they're not the same.

Non-fiction is a book with factual information. Some books, such as comic books or poetry are classified as non-fiction regardless.

Mermaids are a fiction topic. They were first introduced when Greek fishermen caught sight of dugongs, but mistook them for young maidens with the top half being human features, but the bottom half...

No. Realistic fiction indicates that the book is something that COULD happen, not that did happen. If there aren't talking animals or magic spells in it, for example, and it's a story about a kid...