In the US, you're not supposed to say anything publicly that can manipulate the stock price. For a person in Elon Musk's position, it is incredibly easy to drum

In the US, you're not supposed to say anything publicly that can manipulate the stock price. For a person in Elon Musk's position, it is incredibly easy to drum up hype about a stock from a public media source (in this case, Twitter) then secretly sell off stock at the higher price causing it to dip further than it was at before. This is called pump and dumping and is very illegal in the United States (read up on The Great Depression and the stock crash of 1929 for more information).