It sounds to me that you're interpreting that in such a broad way that you could argue that any stock purchases he makes would be in violation of this.
If he's prematurely saying what direction he's going to go one way or another, that's another thing. You don't see Vanguard tweeting "we're going to invest in this company if X happens and divest if not" to the general public, especially if they're trying to influence X to happen.
This essentially why he got in trouble with Tesla for tweeting he wanted to take it private at $420/share, immediately making the stock price jump up, even though he did not have "funding secured" and did not take it private. And he almost lost the ability to be a CEO or on a board of a public company for 10 years because of that!
Because Vanguard is a passive fund. Activist funds do this all the time.