The film, named after the West African kingdom where the treasures were created before they were looted by a French colonel during his conquest of Dahomey in 1892, looks at the response to the return of some of them from Paris to Benin, of which Dahomey is now part.
"To rebuild we must first restore, and to restitute we must do justice," Diop said on accepting the award, highlighting the view of many activists that it is impossible to move beyond colonialism without fully acknowledging the scars it made.
She, like many other prize winners and jury members during a politically charged ceremony, called for a ceasefire in Gaza.
Many others took to the stage wearing the keffiyeh scarf that is a symbol of the Palestinian liberation movement.
The best documentary prize went to Israeli-Palestinian film No Other Land, about the struggle of filmmaker Basel Adra to preserve his West Bank village as Israeli settlers encroach around it.
"I'm here celebrating the award, but also very hard for me to celebrate when there are tens of thousands of my people being slaughtered and massacred by Israel in Gaza," Adra said.
His co-director, Israeli journalist Yuval Abraham added: "I am Israeli, Basel is Palestinian. And in two days we will go back to a land where we are not equal... This situation of apartheid between us, this inequality has to end."
