They figured out how much the average guest paid for drinks, then raised the ticket prices that much but made all drinks free in the park.
It was a huge success. People expect ticket prices to go up occasionally and they expect to be gouged for drinks. By getting "free" drinks, it felt like a huge value. (At least for me when I visited.) I bet it made food sales increase too, because now people wouldn't have to pay for a drink too.
Not sure if they're still doing that, but at the time they also had free sunscreen all over the park. It's an amazing little park.