For Windows applications, the Windows OS inadvertently becomes part of the Controller.
The Model can subscribe to various events/ messages (e.g. mouse click, move, window re-size, button click...). When it has done its change-update-processing the view is updated through the redraw operations.
Windows OS acts as the controller here because it is both sending messages to the model (e.g. mouse click) or to the view (telling it a portion of windows is dirty and needs redraw).
Of course for any commercial application, you would implement your own model and document structures and separate them from the corresponding WinForm objects.
In .net this is not so clear because there is only one file for both the model and view portions. In MFC it was very clear - with a CDocument class and its corresponding CView class.
Rather than the MVC pattern, for Windows applications it helps to understand the Windows messaging architecture and how to handle them.