Final answer:
The narrator disproves the false stereotype that black people are inferior by challenging the association of black people with biblical figure Cain and highlighting the prejudice and disrespect they face.
Step-by-step explanation:
The contemporary false stereotype about 'negroes' that the narrator points out and disproves when the king hears of Oroonoko and Imoinda's reunion is the belief that black people are inferior both physically and morally. This stereotype was perpetuated by associating black people with biblical figure Cain, who was cursed by God and marked with a dark skin tone. The narrator challenges this stereotype by highlighting the unjust prejudice and disrespect that black people face, and arguing for their equal worth and humanity.