I debugged this out of curiosity. All it does is post a message to one of explorer’s windows:
BOOL ExitExplorer()
{
HWND hWndTray = FindWindow(_T("Shell_TrayWnd"), NULL);
return PostMessage(hWndTray, 0x5B4, 0, 0);
}
Of course this is an undocumented WM_USER message so the behavior could quite possibly change in the future.