Violation of fiduciary duty is only a requirement in order to meet the "Manipulative and Deceptive Practices" part of SEC Rule 10b-5.
However there are other ways that requirement can be met for instance SEC v. Dorozhko found that a hacker using stolen information to trade was guilty of insider trading. Obviously he had no fiduciary duty however he was found to be deceptive.
If the SEC prosecute this case I imagine they'd try to extend the argument presented in Dorozhko.
Yes, that's what I was alluding to in my first paragraph. (I did read the article; I am sort of religious now about reading Matt Levine, who is awesome.)
However there are other ways that requirement can be met for instance SEC v. Dorozhko found that a hacker using stolen information to trade was guilty of insider trading. Obviously he had no fiduciary duty however he was found to be deceptive.
If the SEC prosecute this case I imagine they'd try to extend the argument presented in Dorozhko.