loadUserByUsername or by id ?

[wevseen]

In the TwitterUserProvider there's a

 public function loadUserByUsername($username)

which have a $username parameter.

But it is sometimes called with

 return $this->loadUserByUsername($user->getTwitterID()); // TwitterUserProvider.php

and sometimes

 $user = $this->userProvider->loadUserByUsername($accessToken['screen_name']); // vendor\friendsofsymfony\twitter-bundle\FOS\TwitterBundle\Security\Authentication\Provider\TwitterProvider.php

There must be something I don't understand.