Drush cannot find your database connection details
First of all, you should really use Drush 9 or 10 - see https://docs.drush.org/en/master/install/#drupal-compatibility And install Drush site locally as described on the same page.

However, the message Unable to find a matching SQL Class probably means that shared server you are running Drush on is missing the needed PHP database extensions. This is typically PDO with MySQL (pdo_mysql and mysqli) - see https://www.drupal.org/docs/8/system-requirements/php-requirements#database

A typically problem is that PHP in the web server has these extensions, but not PHP on the command line.