Companies typically sell stock to get money (a.k.a. "generate equity"). When they repurchase (a.k.a. "buyback") stock, they are returning that money to the people who gave it to them (a.k.a. "returning equity to shareholders"). Let's examine this more closely using a simple example.
I have no money but have a great idea to make money. I convince you that my idea is great and you agree to give me $1000 in return for 2 shares of stock, each with a 'value' of $500. Remember, those shares really are nothing but paper. You gave me $1000 and I gave you a piece of paper.
However, you're hoping I can do something with your money to create additional value. Still, at the moment you gave me the money, the 'value' of the company was $1000.
Through my business savvy, I succeed and the value of the company rises to $2000. Theoretically, your two shares are now worth $2000 (i.e. $1000 each).
Taking this one step further, you agree to sell one share back to me (as the company) for $1000. You now have your original $1000 back and the company is once again worth only $1000 because $1000 of the company's value was paid back to you. Your one remaining stock is worth $1000 while you received $1000 back from me (as the company).
So, when a company buys back stock, that money goes out the door and cannot be spent by the company since the company no longer has that money.
Think of the original transaction. You gave me $1000. You gave me 'something' for 'nothing'. When a company buys back its own stock, the exact opposite happens. The company is giving away 'something' for 'nothing'.
A stock buyback indicates that the people running the company don't have good ideas to "generate shareholder value". Effectively, when Iger buys back stock, he's saying, "I don't know how to spend the money Disney is making so I'm just going to return it to the investors and let them figure out how to spend it."