except that he did not propose that 'scientific theories' are not factual.
The word theory has 3 different meanings, can sometimes be ambiguous, but its obvious which one is referred to by the context.
Everyone knows what he meant by "its just a theory". he did not say "it's just a scientific theory"
That the commonly used phrase Big Bang theory (probably due to TV show) has the word theory in it does provide an easy opportunity for some to play semantics with, and its about 100% predictable that the first comeback will be about gravity, even though Gravity itself is not a scientific theory.
"Television Host (Graham Chapman): Good evening. Tonight - dinosaurs. I have here sitting in the studio next to me an elk. Aaagghhhh! Oh, I'm sorry, Anne Elk, Mrs Anne Elk.
Miss Elk (John Cleese, as a very prim lady): Miss.
Host: Miss Anne Elk, who is an expert on the...
Elk: No, no, no, Anne Elk.
Host: What?
Elk: Anne Elk, not Anne Expert.
Host: No, no, I was saying that you, Miss Elk, were an, A.N. not A.N.N.E., expert...
Elk: Oh!
Host: ...on elks - I'm sorry, on dinosaurs.
Elk: Yes, I certainly am, Chris, how very true, my word yes!
Host: Now, Miss Elk - Anne - you have a new theory about the brontosaurus.
Elk: Could I just say, Chris, for one moment that I have a new theory about the brontosaurus?
Host: Er... exactly. What is it?
Elk: Where?
Host: No, no, no. What is your theory?
Elk: Oh, what is my theory?
Host: Yes.
Elk: Oh what is my theory, that it is. Yes, well you may well ask, what is my theory.
Host: (slightly impatient) I am asking.
Elk: And well you may. Yes my word you may well ask what it is, this theory of mine. Well, this theory that I have--that is to say, which is mine-- ...is mine.
Host: (more impatient) I know it's yours. What is it?
Elk: Where? Oh, what is my theory?
Host: Yes!
Elk: Oh, my theory that I have follows the lines I am about to relate. (Coughs) Ahem. Ahem. Ahem. Ahem. Ahem. Ahem.
Host: Oh God.
Elk: Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. [Impatient noises from Host] The Theory, by A. Elk. That's A for Anne, it's not by a elk.
Host: Right....
Elk: This theory which belongs to me is as follows. Ahem. Ahem. This is how it goes. Ahem. The next thing that I am about to say is my theory. Ahem. Ready?
(Host moans)
Elk: The Theory by A. Elk brackets Miss brackets. My theory is along the following lines.
Host: Oh God.
Elk: All brontosauruses are thin at one end, much MUCH thicker in the middle, and then thin again at the far end. That is the theory that I have and which is mine, and what it is too.
Host: That's it, is it?
Elk: Right, Chris.
Host: Well, Anne, this theory of yours seems to have hit the nail on the head.
Elk: And it's mine.
Host: (ironical) Thank you for coming along to the studio.
Elk: My pleasure, Chris.
Host: Er...Britain's newest wasp farm...
Elk: It's been a lot of fun.
Host: ...opened last week...
Elk: Saying what my theory is.
Host: Yes, thank you.
Elk: And whose it is.
Host: Yes. ...opened last week...
Elk: I have another theory.
Host: Not today, thank you.
Elk: My theory number two, which is the second theory that I have. Ahem! This theory...
Host: Oh look...shut up!
Elk: ...is what I am about to say...
Host: Oh please shut up!
Elk: ...which, with what I have said, are the two theories that are mine and belong to me.
Host: Look, if you don't shut up I shall shoot you.
Elk: Ahem! My brace of theories, which I possess the ownership of, which belongs to me...
(BANG!)
(Pause)
Elk: Ahem. The Theory the Second by Anne...
(MACHINE GUN FIRE)"