Classical natural philosophy used mizāj (temperament or mixture) to explain features arising from the combination of elements and bodily qualities. Heat, cold, moisture and dryness often featured in these accounts.
Consequences of mixture are properties assigned to such composite bodies. Because these notions presuppose elements, structure and alteration, they are excluded from the divine essence in the theological argument.
These are explanations of historical philosophical terminology, not modern scientific findings. The relevant theological point is freedom from material mixture, composition and change.