Why would an error persist after after uninstalling the module?
This is 'normal' as your Twig files are being cached by Drupal. The easiest way to fix the issue is to run $ drush cache-rebuild (with Drush 8 which is the only release compatible with Drupal 8) which will handle all cache rebuild, including Twig cache. Alternatively, under sites/default/files/php you can safely delete the twig directory. If you're not in a multi web server environment, you can delete the php directory altogether, which will both delete the Twig cached files and the Service Container.