Technically this isn't false advertising, at least in legal terms. In order for an ad to qualify as false advertising you need:
- A statement of fact that is false
- The false statement has to deceive or have the potential to deceive a substantial portion of the target audience.
- The false statement has to affect the purchasing decisions of the audience
- There is proof of actual loss from the false advertisement
Showing people dining with Princesses qualifies as #1. It would be pretty hard to prove #2 but I would assume the vast majority of viewers know they can't actually dine with a princess. Without #2 the 3rd and 4th criteria are out too. If there was any chance Disney could be held liable for false advertising someone would have sued them long ago. People sue Disney all the time.
The ads are not intended to deceive people into thinking they can eat with a princess or ride an empty roller coaster alone. They are using artistic license to try to sell a feeling or an attitude. The Wizarding World of Harry Potter ads for the new land in Hollywood show a girl in the park take out a wand and point it at the castle and all of the lights come on. They aren't telling you that you can do magic or turn the lights on if you go there. It can't be taken literally.