When you write a call as a seller you essentially take a short position against the stock delta wise[.] When SoftBank bought loads of calls that were out of the money then the writers had large negative delta positions against these tech stocks.
One common way to offset a negative delta is you can hedge with owning shares to offset the negative position from the calls you write. As the calls were heavily wrote then shares were added to offset risk which contributed towards momentum. As the stock positions were entered it drove up price of stock which put those out of the money options closer to the money leading to more share purchases while SoftBank continued to purchase more and more calls leading to an increased share price between delta hedging and general market momentum. Someone can correct me if I’m off but that’s my broad description