The discussion seems to ask first of all to differentiate between what is the human being made in the image of God, and, on the other hand, what humanism is. I think it is two different things because to affirm that the human being is made in the image of God means that God creates the human being in his image, as if he were a copy of God, therefore, in the human being there is something divine, of God, but as a copy, as an image, not as an original. On the other hand, humanism is a cultural and philosophical movement that places the human being at the center of the Universe. There can be different humanisms, for example Marxist, Christian, atheist, among others. It would be appropriate to clarify what humanism the question refers to. If, for example, we accept that God is a personal God and that he creates human beings in his image, then we seem to be dealing with a Christian humanism. From this point of view, it seems that God is a humanist because his most important work is the human being, a copy of him.