Truth goes deeper than fact. Truth can transcend both fiction and fact. Fiction can express truth as effectively as fact and sometimes better.
For example. a great novel such as Silas Marner can reveal truths about the human heart that are rarely found in nonfiction writings.
However, the story in a novel or work of fiction is not something that really happened, or it did not happen in the way it is told in the story. It is not true in that sense.
Nonfiction writing is true in the sense that it represents facts, or is purported and believed to represent them; but you can gather many facts together and still not have a true picture, and you can present facts in an interpretation that distorts them or even makes them completely false in their effect. The newspaper, for example, is presumed to present facts objectively; but the simple act of being selective in which facts to include can change the way a story is understood, and the language that a reporter chooses in presenting those facts greatly influences the way it is received. Consider, for example, the phrase "freedom fighters." Suppose instead the writer referred to those same rebels as "outlaw insurrectionists." How does that change the impression given to the reader?
Choice of language reflects a point of view and expresses an opinion unless the writer takes great care to keep it neutral. And--is a completely neutral, noncommittal recital of facts really more true than writing that reveals the heart of the writer?
This is a big question and not one that is easily answered. You can't draw a line and say that fiction is on one side of it and truth is on the other, or that fiction is on one side and fact is on the other and that truth is on both sides. You can have both fact and fiction that lack any truth. They are different qualities, just as color and shape are different qualities.