\( element1, element2, ... ) takes a reference to each element in the list and returns that list (i.e. ( \element1, \element2, \... ) whereas [ element1, element2, ... ] returns a reference to an array containing those elements.

When you push the results of taking a refererence to a list into @fibble, you add a reference to each element in the list individually, as opposed to adding a reference to an array containing those elements as you do using the anonymous array composers [].