Simplest way to verify, launch visual studio 2015, press Tools/Spy++, in Spy++ find the visual studio’s main window, you’ll see that Win32 thinks visual studio is a single window with no children, with class starting with “HwndWrapper[DefaultDomain;”

Unlike that, Spy++ itself uses Win32 (wrapped by MFC but it doesn’t matter) for GUI, you’ll see these SysTreeView32, msctls_statusbar32 and other native controls there.