Briefly;
Disney is a publicly held company - if Comcast buys enough stock from current stockholders, it "owns" the majority of the company.
If the Board of Directors agrees with the sale and the price per share, and recommends it, the sale becomes an acquisition - happens all the time - and most of the shareholders go along.
If the BoD does NOT agree with it, the sale becomes an attempted hostile takeover; the purchaser then has to offer a stock price that will tempt the stockholders to disregard the BoD's recommendation.
There are steps that the BoD can take to make a hostile takeover more painful to the purchaser, but that's another post....