The Array plugin internally maintains a 3D array at all times, even if it's only used 1-dimensionally. This means it's neither much use to expose it directly (since few libraries expect a 3D array), nor is it convenient for calling code to have to worry about maintaining the right structure of the array. So it exposes several accessor methods that allow you complete control over the array but guarantee you can't mess up the structure. So just use these to flatten to a 1D array or whatever else you want to do.
The Array plugin ID is "Arr" not "Array".