That is as bad an anology as I have read or heard anywhere.
It's not THAT bad, a better one though might be with regards to computers. People will buy a Dell (or used to) and say "I have a Dell!", but the parts behind it are not Dell's at all, they're Intel, ASUS, etc.
Or how about this one, American car companies have made cars using Japanese engines, so is the car a Japanese car? Without the engine it's not going anywhere, but the American logo is slapped on the front of the car. Since Bethesda/Zenimax created the original Fallout 3 (the "Engine"), Obsidian just built around it (the body, the frame, the steering column, etc, etc), so by your logic, it's Bethesda's game. By car logic, that's Ford's car, even if it's a Honda engine in it.
I don't really care either way.