Elon Musk is not capable of acting as a fiduciary to anyone but himself. He violated SEC rules to pad his own profit as he bought up his 9.2% stake in Twitter, just like he used Twitter to pump up the stock price of his other businesses.
Musk is a true proponent of free speech, which he recognizes is absolutely essential to a functioning democracy. He knows all too well that big tech and mainstream media are dominated by rich people who use them to advance their own political objectives. He was simply trying to use his leverage as an investor to make Twitter adhere to its own policies and stir the pot a bit.
We haven't heard the last of the Musk and Twitter saga. By refusing a seat on the board, Musk was able to change his status with the SEC, a move that will allow him to continue to enlarge his stake in the company and to pursue real reforms.