Do you have any proof of that?
All of those statements are matters of opinion, so of course there's no proof.
But I can't see that there's much doubt that Keegan didn't like working to a DOF. He'd stayed away from the game for three years and not been to a single match, so the idea that he was disillusioned with football isn't a wild one. His company wasn't doing well so again it's not exactly sticking your neck out to say that that influenced his decision to return. Not to mention he quit after only a few months in circumstances that are still unclear.
The most logical explanation is that his motivation was always a bit brittle. Not for the first time either.
Yet despite his company supposedly struggling, he still chose to walk away from the sport that he loves. Says everything about football as a whole, never mind just NUFC.