One thing, I've seen it so many times. Second, there's no logic behind it.
The problem with these things is, people like the idea and make a run of it. Journalists are actually morally responsible for vetting their stories, but they often don't, instead writing what people want to believe because it sells copy. The world is sometimes a very primitive place...
So the Stappert quote of Höttinger driving an ATS at the Austrian GP in 1980 is a fake, he never said so?
My understanding is the driving force behind Höttingers ambitions towards F1 might be indeed not BMW but the people working in the motorsport department. BMW pulled the plug on their F1 ambitions at the end of 1979 as you stated in a post earlier. But wasn´t there a strong opposition in the motorsport department working (finally successful) as a "Guerilla Force" against that decision?