I think its an Idiom. I don't see like or as. So no simile. I don't see he is something like a marshmallow. - No metaphor. I also don't see a non-human thing doing human things- the grass was dancing in the wind. My answer would be an idiom.
Hemingway was driving an ambulance in Italy not because he had been injured or because he was a doctor, but because he was assisting the Red Cross on the Italian front.
Hemingway first served in World War I and later lived in Paris. He also wrote A Farewell to Arms after the war and drew on his personal experiences to do so. Finally, he retired to Key West.
Hemingway's writing style was anything but commonplace or boring. In fact, it was the lack of wordiness and the creative succintless that made Hemingway's works so popular.
