Was that in the biography? I don’t remember although it was a long time since I’ve read it. One thing I remember is Tolkien describing himself and us as sub-creators to the one creator, God. That having imparted his spirit into us we also have the desire to create. So he created his land of Middle Earth and all the creatures in it. Middle Earth, being in the middle, between Heaven and Hell.
He discusses subcreation in Tree and Leaf, an essay.
I’ve always thought that the ability to imagine and create from imagination is what makes us ‘in His image’.