Integrating with Paypal Stage 5 problem

I'm redoing this track so I'm clear about how to do this stuff but I came across this question and I don't get it:

I visit my flavor.php file with an extra variable in the web address, like this:

http://localhost/flavor.php

If my flavor.php file has the code shown below, what does it output?

<?php

$flavors = array();

$flavors[1] = "Cake Batter";

$flavors[2] = "Cookie Dough";

if (isset($_GET["id"])) {

    if (isset($flavors[$_GET["id"]])) {

        echo $flavors[$_GET["id"]];

    } else {

        echo "B";

    }

} else {

    echo "A";

}

?>

There is no extra variable in the URL and thus $_GET["id"] can't be set, so (as I see it) it should skip the code block and run the first else statement, meaning the answer would be B but it's not.

$flavors is obviously set but I can't see how it would use it if the other part of the statement can't be applied unless it's ignoring it, which is not something I've come across in any of the examples. I'm curious what I'm missing here. If someone could elaborate I'd appreciate it.