What is the difference in how you would have to access these two PHP arrays?

I have two PHP arrays in a section of a website I'm building for a class. One contains data that I created with a simple foobar array bit, and the other is created from a fetchAll() PDO call. I can't access the PDO array's element for some reason, so I created a sample array and called var_export() on both arrays to see if there were any differences. Here is the code:

if ($dao->userExistsLogin($_POST["email"], $_POST["password"]))
{
    $useremail = $_POST["email"];
    $_SESSION["authenticated"] = "true";
    $logger->LogDebug("email from post array in login handler: " . $_POST["email"]);
    $user_results = $dao->getIDFromEmail($useremail);
    $logger->LogDebug(print_r($user_results, true));
    $array = [
        "foo" => "bar",
        "bar" => "foo",
    ];
    $logger->LogDebug(var_export($array, true));
    $logger->LogDebug(var_export($user_results, true));
    $logger->LogDebug(gettype($user_results));
    $_SESSION['user_id'] = $user_results['id'];
    header("Location: http://localhost/WIWO/user_account.php");
} 

The GetIDFromEmail function is here:

    public function getIDFromEmail($email)
    {
        $conn = $this->getConnection();
        $getIDFromEmailQuery = "SELECT * FROM user WHERE email=:email";
        $query = $conn->prepare($getIDFromEmailQuery);
        $query->bindParam(":email", $email);
        $query->execute();
        $result = $query->fetchAll(PDO::FETCH_ASSOC);
        $this->logger->LogDebug(print_r($result, true));
        return $result;
    }

And here's what's in my logger from the var_export() commands:

2020-10-31 17:57:10 - DEBUG --> array (
  'foo' => 'bar',
  'bar' => 'foo',
) 
2020-10-31 17:57:10 - DEBUG --> array (
  0 => 
  array (
    'id' => '251',
    'email' => 'heck',
    'institution' => 'heck',
    'access' => '1',
  ),
) 

Why can I not access the second array at $_SESSION['user_id'] = $user_results['id'];? For some reason that line totally fails to do anything. I know the session is started and correct because other variables stored in the SESSION superglobal are showing up correctly, but the user_id never gets set. Does it have something to do with "0 =>" showing up in the var_export() of the second array? I notice that doesn't show up in the first array - is the second array malformed or something?