Using flatMap in Webservice

[yoching]

I watched this video. Great talk! Thank you!

In the video ( at about 8:07) , flatMap is used in load method of Webservice like this. (Actually, I copied this code from the article.)

final class Webservice {
    func load<A>(resource: Resource<A>, completion: (A?) -> ()) {
        NSURLSession.sharedSession().dataTaskWithURL(resource.url) { data, _, _ in
            let result = data.flatMap(resource.parse)
            completion(result)
        }.resume()
    }
}

However, in this sample code, flatMap is not used and guard let is used instead. Are there any reasons that this sample code does not use flatMap?