According to Columbia Law Professor Tim Wu, an expert on copyright and corporate media law writing on the New Yorker's Culture Desk blog, the film falls under the "commentary and parody" provisions of the fair-use exception for legal use of copyrighted materials. He makes a link to a similar high-profile case.
A famous case over the artist Thomas Forsythe’s “Food Chain Barbie” series is similar to this one. In the late nineteen-nineties, Forsythe created a line of artistic photographs of Barbie under attack by various vintage appliances. According to Forsythe, he wanted to “critique the objectification of women associated with [Barbie], and to lambast the conventional beauty myth and the societal acceptance of women as objects because this is what Barbie embodies.” His work made just thirty-seven hundred dollars, but Mattel sued for both copyright and trademark infringements. The courts threw out the complaints under a fair use and First Amendment rationale. The judges were so annoyed by the lawsuits that they awarded attorney’s fees of nearly two million dollars to the artist.
Wu's essay is definitely worth a read, as it makes a larger case for the importance of these instances of fair use. (He ends by saying "a world where Disney gets to determine everything said about Disney World would be a poor place indeed.)
While the precedent and its $2 million penalty for bringing the case make it seem less likely that Disney will raise a fuss, $2 million is just a slap on the wrist for the massive company. Disney is, of course, staunch supporters of its copyright holdings, lobbying so devotedly for the 1998 Copyright Extension Act that it was dubbed the Mickey Mouse Protection Act.