Of course this is price manipulation. Bitcoin is already responding to Elon's mentions! And the price of any altcoin is guaranteed to change significantly. If you have a lot of money and an army of followers, this is the easiest way to earn many millions of dollars))
It's hard to mobilize an army for it if someone isn't as rich as Elon Musk, because people will tend to look at who we really are and also what assets we already have, so nobody will be able to do a job like Elon Musk at this point.