Comment by Forricide

> Yes, the application hasn’t quit. You’ve only closed its last window.

To further expand on this, this is also application-defined behaviour. The application can choose whether it wants to stay open or close. This is no different from Windows (e.g. closing a Spotify window will just minimize it to taskbar), it's just that Cmd+Tab by default shows all running applications, whereas Win+Tab/Alt+Tab on Windows by default shows open windows.