Rather than explaining the food falling from the sky, I'd have rather seen something that actually is relevant to the book more. Create a few main characters (maybe a family) living in Chewandswallow and showcase at first their everyday lives, and then move on to the conflict of the story, the increasing storm of food. Show some story about how that particular family is adjusting to the problems, have hilarious moments with the food falling on things, have heartbreaking moments where a main child is scared about the storm, add some examples from the book about specific food falling and let the characters react to it. If done right, you really could have made a nice plot with a combination of humor and heart based on the events from the book.
The movie, while showing some elements of the book, just wanted to make this fictional mash-up explaining what was really going on in the town and during the storm rather than putting aside the logic and telling the fantastical story that we have all come to love.