Lesson 9 Lottery: How does performUpkeep() actually call the fulfillRandomWords() function?

[BorisRy]

My code compiles and I'm already at the tests part, but now that I go back to the contract I don't understand how the performUpkeep() function calls the fulfillRandomWords() function. What am I missing? There's no function call for fulfillRandomWords() inside performUpkeep().

 function performUpkeep(
        bytes calldata /*performData*/
    ) external override {
        // checkUpkeep returns two values and takes one value
        (bool upkeepNeeded, ) = checkUpkeep("");
        if (!upkeepNeeded) {
            revert Raffle__UpkeepNotNeeded(
                address(this).balance,
                s_players.length,
                uint256(s_raffleState)
            );
        }

        s_raffleState = RaffleState.CALCULATING;
        uint256 requestId = i_vrfCoordinator.requestRandomWords(
            i_gasLane, // gasLane
            i_subscriptionId,
            REQUEST_CONFIRMATIONS,
            i_callbackGasLimit,
            NUM_WORDS
        );
        emit RequestedRaffleWinner(requestId);
    }

    function fulfillRandomWords(
        uint256, /*requestId*/
        uint256[] memory randomWords
    ) internal override {
        uint256 indexOfWinner = randomWords[0] % s_players.length;
        address payable recentWinner = s_players[indexOfWinner];
        s_recentWinner = recentWinner;
        s_raffleState = RaffleState.OPEN;
        s_players = new address payable[](0);
        s_lastTimeStamp = block.timestamp;
        // Send winner the money
        (bool success, ) = recentWinner.call{value: address(this).balance}("");
        if (!success) {
            revert Raffle__transferFailed();
        }

        emit WinnerPicked(recentWinner);
    }

[PatrickAlphaC]

performUpkeep calls requestRandomWords - which kicks off a Chainlink VRF Request.

A chainlink node later will then respond by calling the fulfillRandomWords function!

Feel free to watch the walkthrough: https://www.youtube.com/watch?v=rdJ5d8j1RCg