return array but why suddenly object -- cache_get question

First, we see $cached is an object returned from cache_get function in

  if ($cached = cache_get('variables', 'cache_bootstrap')) {
    $variables = $cached->data;
  }

But from function getMultiple inside cache_get function

 foreach ($result as $item) {
        $item = $this->prepareItem($item);
        if ($item) {
          $cache[$item->cid] = $item;
        }
      }
//--
return $cache;

Showing that $cache is an array.

So we see there is a sudden change from array to object.
Can some one help us to make it clear.

Thanks and Regards.