Can't solve 'Implement MYSQL RepositoryInterface' objectives. is this a bug?

I’m struggling to solve this problem under 'Implement MYSQL RepositoryInterface'.

Link to challenge (task 2 of 3)

The question and my code is as follows:

Question:

Challenge Task 2 of 3 Define the "all" method to return all items from the MySQL database table passed to the method. Use "fetchAll(PDO::FETCH_OBJ)" to return the results as an array of objects.

Code:

<?php

class sqlRepository extends PDO implements RepositoryInterface
{
  private $pdo = null;
  public function __construct($dsn)
  {
    try {
      parent::__construct($dsn);
    } catch (\PDOException $e) {
      echo $e->getMessage();
    }
  }
  public function all($table)
  {

    //$this->posts = $table;
    //var_dump($table);
    $stmt = $this->query('SELECT * FROM '.$table);
   // $stmt = $this->prepare('SELECT * FROM ?');
    //$stmt->bindValue(1, $this->posts);
    var_dump($stmt);

   // $stmt->execute(array(1, $this->posts));
    //$stmt = $this->query("SELECT * FROM posts");
    $results = $stmt->fetchAll(PDO::FETCH_OBJ);
    var_dump($results);
    return $results;
  }

}
// var_dump(scandir(__DIR__));

Everytime I try to prepare a statement with the $table parameter the pdo statement returns a false bool. Concatenating the variable with the query seems to return the expected result from the db but whenever I check the work I get this weird feedback:

“Bummer: Argument 1 passed to enroll() must be an instance of Student, string given </span></pre>”

Is this a bug? Or am I doing something wrong here? Any help would be greatly appreciated.