From Documentations:

Register a service constructor, which will be invoked with new to create the service instance. This is short for registering a service where its provider's $get property is the service constructor function that will be used to instantiate the service instance.

I think this is technically wrong, because as stated in Docs, "An Angular service is a singleton object created by a service factory". So service method is a shorthand for registering a service where its provider's $get property is a function that returns an instance created by the service constructor, not the constructor itself.
This is exactly inline with the code for $provide.service:

function service(name, constructor) {
    return factory(name, ['$injector', function($injector) {
      return $injector.instantiate(constructor);
    }]);
  }