alt Hacker Newsctrl-f4 is used in MDI applications to close one document window of a multi-document application. alt-f4 to close the whole application.
Well, I say "is used", but nothing in Windows is consistent anymore. Especially since web browsers started disrespecting the OS shortcuts. Now it seems like every application follows the web browser UI conventions instead of OS ones.
Alt+F4 in Windows has always been "close window", not close app. It is even shown on the traditional "application icon" menu on each window, that many new apps are unfortunately doing away with.