Bellotti represents the Commonwealth of Massachusetts' attempt to limit corporate speech on a matter of public policy. In this case, it was the state legislature's desire to get a state personal income tax approved by referendum. These corporations very much were expressing their opinions on a matter that did not directly affect them.
Quoting from the first sentence of Wiki's article on Bellotti:
First National Bank of Boston v. Bellotti, 435 U.S. 765 (1978), is a U.S. constitutional law case which defined the free speech right of corporations for the first time.
Yes, I know, Wiki is not the best source but it tends to do a reasonably well job of explaining legal decisions in laymen's terms.
Disney not only stated their opposition to the law but also stated their intention to use company resources to oppose the law, similar to what happened in
Bellotti.
Bellotti directly applies to what happened to Disney.