Approved by who, exactly? Ubisoft own everything Assassins Creedy, they paid for this film and did it themselves, basically... Their money, their franchise, their intellectual property, to do with whatever they want, no-one else's approval needed....
They could make it into midget-clown porn, if they so chose... which might actually have been a better move than the AC3 story of Connor Rahonapocahontahonkeytonke Kenway...
AC3 had the best story of any AC game ever imo (except for the rushed final chapter). Not that this is too difficult, considering how low the serie has fallen in terms of storytelling since then.