This "nothing immaterial" does not refer to the non-existence of a Form, as component of the Matter-Form composite. A human being is a composite of Matter and Form, but here "Form" refers to all essential content (all determination) of that human being, all the way down to Prime Matter, the carrier of all content. So "Form" here includes, to be sure, Mind, but not exclusively so.
Hence this case (the case of the ontology of a human being) is no different from that of any other concrete thing.