He posted a meme and his position. He said absolutely nothing incriminating in his livestream.
That is probably true. Nevertheless this is America where everyone is suing their mother. So as a HF lawyer I could make an argument that a famous person can move (aka manipulate) the market just by disclosing positions. And that is true in the case of RK. Now if he actually traded (maybe not) against those statements and movements, that could count as market manipulation.
