You are using the word theory wrong. (or rather you are conflating the scientific use and the colloquial) A scientific theory must have some explanitory power (eg the big bang explaining cosmic background radiation etc) God has none of this. There is no explanation with "God did it". We can't make and predictions and test them based on God as the answer. The colloquial use of the word as an unproven guess is more like a scientific hypothesis than a theory