We can't prove God exists, we don't even have evidence that he does, so I think calling God a theory is extremely generous.
Taz will have to explain his thought process. I teach science, so I have this tendency to think of a theory as something that explains observable facts. In this way, I can take a teaching (heard or written), apply it to a situation, and observe what happens.
I would not got up to a person and say, "You are a theory." About the best I could do is say, "You walk, talk, and look like a person. Therefore my theory is that you are a human being."
I'm sorry about this, because I also teach grammar, and you and Taz may think I am picking at straws, when what
I'm really am is a good example of an out of control grammar police.
Still, I am unsure of Taz's statement.
"The earth was created by God," qualifies as a theory. It explains a fact (the earth exists). Throughout history, we have stories of people who felt they were being cared for, or taught, by something spiritual/supernatural, not physical. Right away, we may run into a problem using the word 'theory', if nothing was observable. Still, we might catch the meaning if someone said, "Because of spiritual healing, I theorize there is a God."
But God himself is not a theory. A theory explains an observable fact. I haven't seen God explaining observable facts lately, therefore He is not a theory.
Yes, I know! The workings of my mind can take one aback.