He bought twitter since he is already tired on twitter censorship. He wants to give freedom not a manipulation so that everyone can be free to express there opinion on anything especially political views. He can’t manipulate the market by just using Twitter because there’s other social media channel that can be use to share information while manipulation is clearly using all the social media channel to control the news.
People is just dumb enough to use Elon statement as signal for there trading activity. Elon is just sharing his thoughts while people speculate base on it. A real manipulation is when someone gives you advice for your next action such as buy DOGE. Speculation is what makes it looks like a manipulation. Price will not move in either direction if no one will speculate to his post that has no direct mention crypto.