DevDocs example for Creating a Magento admin page throws error

[JoAnne4WDT]

  namespace WDT\Faq\Controller\Adminhtml\Menu;
  class Index extends \Magento\Backend\App\Action
  {
    /**
    * @var \Magento\Framework\View\Result\PageFactory
    */
    protected $resultPageFactory;
    /**
     * Constructor
     *
     * @param \Magento\Backend\App\Action\Context $context
     * @param \Magento\Framework\View\Result\PageFactory $resultPageFactory
     */
    public function __construct(
        \Magento\Backend\App\Action\Context $context,
        \Magento\Framework\View\Result\PageFactory $resultPageFactory
    ) {
         parent::__construct($context);
         $this->resultPageFactory = $resultPageFactory;
    }
    /**
     * Load the page defined in view/adminhtml/layout/faq_menu_index.xml
     *
     * @return \Magento\Framework\View\Result\Page
     */
    public function execute()
    {
         return  $resultPage = $this->resultPageFactory->create();
    }
  }

That's my index.php for a module I'm trying to add to the admin pages. When I click the link to open that page, it throws me an error :

PHP Fatal error:
    Uncaught TypeError: Argument 1 passed to WDT\\Faq\\Controller\\Adminhtml\\Menu\\Index::__construct()
    must be an instance of Magento\\Backend\\App\\Action\\Context,
    instance of Magento\\Framework\\ObjectManager\\ObjectManager given,
    called in /var/www/html/shop/vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php on line 93
    and defined in /var/www/html/shop/app/code/WDT/Faq/Controller/Adminhtml/Menu/index.php:17

AFAIK I followed the steps as layed out in http://devdocs.magento.com/guides/v2.1/ext-best-practices/extension-coding/example-module-adminpage.... but it keeps giving me that error. And I don't know what I am doing wrong. Cleaned the cache, Ran setup:upgrade, then ran setup:di:compile, but nothing changes. Is the example as given in DevDocs omitting something that I should know ?