What you have is an array, of which each element is a type defined cluster. The array contains the cluster. When you right click the array and open the type definition, it opens the element definition, which is a cluster. The item on the block diagram is an array that contains that cluster type as the array element.
To generate the same thing yourself, drop an array constant on the block diagram. Then drop the cluster type definition onto the block diagram as a constant. Drag the cluster into the array and you'll see the result matches what you already have.