The technique is equivalent to collage. Assenbling bits and pieces in a new context, to mean something different. An excellent and well-established technique in art and literature. Not at all the same as plagiarism.

Actually Woody didn't take John Steinbeck's book as his source, he took the film made from it. Explaining that a lot of the people it was about would never get to see the film (and certainly never read the book - I've never read the book.)   And then Bruce Springsteen did the same, using Woody's song as the jumping-off point (at least I think that's how it worked), with The Ghost of Tom Joad.