It's illegal to purchase a stock and announce you purchased said stock?
Obviously it's not strictly illegal to purchase stock and then say you did, but it doesn't make sense that you would need that clarified.
Financial transparency isn't illegal by itself.
Also, if what Tesla did was illegal then aren't many authors on Bloomberg/SeekingAlpha/ CNBC/etc also just as liable? Seems like what we're discussing is a common occurrence and securities cases are often about people misleading about their own stock/company rather than third party/other tickers (even if they hold shares, or in this case coin).