Due to the big investment made by Tesla, and the acceptance of bitcoin as a method of payment, it is more like having a high side of their shares on bitcoin, which now makes them to be in a close trend with that of bitcoin, being affected with the price movement of bitcoin.
In terms of Tesla Elon Musk to control the market, that is not possible, he is a big time investor in bitcoin, so are there big time whales also existing in the market. What Tesla Elon Musk can do is to make a withdrawal of His profits, which could reduce the price as a normal thing that is been done by whales and big holders of bitcoin.