What does that mean? I've seen it stated a few times but not sure how it ties in with Twilight books/movies?
The author wrote it as a fan fiction. She took the Twilight characters of Edward and Bella and made it into a story of her own, then changed the names of the main characters.
Background
http://en.wikipedia.org/wiki/Fifty_Shades_of_Grey#Background
The Fifty Shades trilogy was developed from a Twilight fan fiction series originally titled Master of the Universe and published episodically on fan-fiction websites under the pen name "Snowqueen's Icedragon". The piece featured characters named after Stephenie Meyer's characters in Twilight, Edward Cullen and Bella Swan. After comments concerning the sexual nature of the material, James removed the story from the fan-fiction websites and published it on her own website, FiftyShades.com. Later she rewrote Master of the Universe as an original piece, with the principal characters renamed Christian Grey and Anastasia Steele and removed it from her website before publication. Meyer commented on the series, saying "that's really not my genre, not my thing... Good on her—she's doing well. That's great!"
Reception
http://en.wikipedia.org/wiki/Fifty_Shades_of_Grey#Reception
Aside from a smattering of sympathetic reviews, critical reception of Fifty Shades of Grey has been generally negative, with most critics noting poor literary qualities of the work. Sir Salman Rushdie said about the book: "I've never read anything so badly written that got published. It made Twilight look like War and Peace." Maureen Dowd described the book in The New York Times as being written "like a Bronte devoid of talent," and said it was "dull and poorly written." Jesse Kornbluth of The Huffington Post said: "As a reading experience, Fifty Shades...is a sad joke, puny of plot".
Controversies
Origin as fan fiction
http://en.wikipedia.org/wiki/Fifty_Shades_of_Grey#Origin_as_fan_fiction
Fifty Shades of Grey has attracted criticism due to its origin as a fan fiction based on the Twilight novels, with some readers predicting copyright issues due to this connection. Amanda Hayward of The Writer's Coffee Shop responded to these claims by stating that Fifty Shades of Grey "bore very little resemblance to Twilight" and that "Twilight and [the] Fifty Shades trilogy are worlds apart".
In April 2012, when E. L. James was listed as one of Time magazine's "100 Most Influential People in the World", Richard Lawson of The Atlantic Wire criticised her inclusion due to the trilogy's fan fiction beginnings.
The fan fiction origins of the book were an issue in a lawsuit where Universal Studios attempted to prevent the release of a pornographic film based on it. The porn producer claimed that "much or all" of the Fifty Shades material was placed in the public domain in its original Twilight-based form, but later capitulated and stopped production of their film.