This:
$rows = array(
      array( 
        array('data' => t('Type'), 'header' => TRUE),
        array('data' => t($watchdog->type))
      )
);

Should look like this:
$rows = array(
      array( 
        array(
           'data' => t('Type'), 
           'header' => TRUE
        ),
        array('data' => t($watchdog->type))
      )
);