Short and Simple
"The Revolutionist" is eight paragraphs long, and three of these paragraphs are only one sentence long a piece. So yeah, this one's short. And the language Hemingway uses is simple. You might even call it sparse. Check out this example:
He was a Magyar, a very nice boy and very shy. Horthy's men had done some bad things to him. He talked about it a little. (3)
This is a pretty understated way of saying that the comrade has experienced some brutal political violence, is maybe a bit scarred/traumatized by it, and has a hard time talking about what happened to him. By giving us such limited details, Hemingway compels us to imagine what might have happened to the comrade in Budapest, how he feels about it, and how hard it is to relate those experiences. Pretty cool, right? We think so anyway. Way to be economical, Hemingway.