Not can Elon Musk just manipulate the market, but his influence transcends from every investor which ultimately controls the prices of either the stock or the cryptocurrency market.
I remember, Elon Musk tweeted about his support on DogeCoin and its price skyrocketed. When Elon also expressed his opinion about BTC, its price decreased. His influence in the market controls the decision of most investors since they believe in his motive.