It has been saying that in the booklet since day one. it's poorly worded and confusing. They have no problem with people bringing beverages onboard. They have had problems with people bringing those hardsider 'Igloo' type coolers. Here's a cut and paste from a soon to be done faq on the subject.
First, NO ice! Ice can mess up the scanner and they will make you dump it all out before letting you in. Don't worry, ice is available on Deck 9 at the drink station and your room steward will bring as much as you want, up to three tiems a day!
Second, The size of your carry on must fit through the scanner to get into the terminal and on the ship after excursions. Disney uses an airport type scanner. The average size for one to fit is 22 inches long by 14 inches wide by 9 inches thick. It can't be much bigger than that.
