The letter does not say anything about extra activities. It specifically says alternative opportunities. That is marketing talk for saying "some of the stuff we normally have here is not available here because of construction, but you have the alternative opportunity to go to the Contemporary or Fort Wilderness to do those things if you want to, so while it is temporarily unavailable here, it is still available to you, you just have to go next door to do them."
Of course, the other alternative is just not do them. These things include mostly things like volleyball net and lounge chairs at the beach area and marina stuff like boat rental, waterskiing, fishing, parasailing etc...and these things are also available to non resort visitors.
We often visit other resorts and do stuff at resorts we are not staying at. For example, you can go to any resort and watch the evening movie. You don't have to be staying there. You can watch the fireworks from the monorail resorts without staying there. You can eat at any of the resorts without staying there. The people at the marina that rents you a boat don't care if you are staying there. Off site customers who visit the resorts and spend money are quite welcome as the dollar they spend is still a dollar.