Did the Ba'ku really need to say they calimed the planet?
They settled on it prior to the founding of the Federation.
So when the Federation found it, it was aready inhabiated by a seemingly non-warp culture as such the PD would apply at it would be ignored.
The situation is similair to an episode of TNG where Worf's adoptive brother was to transplant a group of people to save them. A clear violation of the PD. In INS they want to move a group of people to get at something, still a violation of the PD.
It seems clear from the movie that the council wasn't told the full story, and as soon as they had been updated they reveresed their earlier ruling.