His mother would have to be 19. She was only 18. If born in Kenya, he wouldn't qualify for dual citizenship. However he did admit Kenyan citizenship through his father.
As to dual citizenship: The Hague convention (1930) state that both countries must agree to joint citizenship.If one does not than only one can claim. He could possibly have had joint with Kenya as they were part of the British Empire.
However, when his mother married Soetoro and moved to Indonesia. His step father enrolled him into public school % states he was the father (No official adoption paper is necessary there). Public school there did not allow non-citizens to enroll. Since, Indonesia does not recognize joint citizenship, therefore, he lost his US citizenship.
Later (in his 20’s) he traveled using the INDOnesian passport into countries that people with American citizenship (poassport were not allowed to travel to. (Clue listen to haow he pronounces Pakistan.)