invalid_localhost test in helo plugin?

How can this ever pass when receiving mail from the outside?

sub invalid_localhost {
    my ($self, $host) = @_;
    if ($self->is_localhost($self->qp->connection->remote_ip)) {
        $self->log(LOGDEBUG, "pass, is localhost");
        return;
    }
    if ($host && lc $host eq 'localhost') {
        $self->log(LOGDEBUG, "pass, host is localhost");
        return;
    };

    #$self->log( LOGINFO, "fail, not localhost" );
    return "You are not localhost", "invalid localhost";
}

What is the relation between the helo and fcrdns plugins? Isn't helo doing everything and more than fcrdns does?