Answered addPackage called with an invalid package name. Yet, I should be passing the conditions.

     /**
     * Adds a model package and base class path for including classes and/or maps from.
     *
     * @param string $pkg A package name to use when looking up classes/maps in xPDO.
     * @param string $path The root path for looking up classes in this package.
     * @param string|null $prefix Provide a string to define a package-specific table_prefix.
     * @return bool
     */
    public function addPackage($pkg= '', $path= '', $prefix= null) {
        $added= false;
        if (is_string($pkg) && !empty($pkg)) {
            if (!is_string($path) || empty($path)) {
                $this->log(xPDO::LOG_LEVEL_ERROR, "Invalid path specified for package: {$pkg}; using default xpdo model path: " . XPDO_CORE_PATH . 'om/');
                $path= XPDO_CORE_PATH . 'om/';
            }
            if (!is_dir($path)) {
                $this->log(xPDO::LOG_LEVEL_ERROR, "Path specified for package {$pkg} is not a valid or accessible directory: {$path}");
            } else {
                $prefix= !is_string($prefix) ? $this->config[xPDO::OPT_TABLE_PREFIX] : $prefix;
                if (!array_key_exists($pkg, $this->packages) || $this->packages[$pkg]['path'] !== $path || $this->packages[$pkg]['prefix'] !== $prefix) {
                    $this->packages[$pkg]= array('path' => $path, 'prefix' => $prefix);
                    $this->setPackageMeta($pkg, $path);
                }
                $added= true;
            }
        } else {
            $this->log(xPDO::LOG_LEVEL_ERROR, 'addPackage called with an invalid package name.');
        }
        return $added;
    }

$prefix = 'xyz_';
$packagename = 'moarDataStuff';
$classname = 'Grows';

$packagepath = $modx->getOption($packagename . '.core_path', NULL, $modx->getOption('core_path') . 'components/' . $packagename . '/');
$modelpath = $packagepath . 'model/';

// The variable has been swapped out for a static string to make sure.
$modx->addPackage('moarDataStuff', $modelpath, $prefix);

$grow = $modx->getObject( $classname, array( 'grow_id' => $_GET['id'] ));

$this->log(xPDO::LOG_LEVEL_ERROR, 'addPackage called with an invalid package name: '.$pkg);