[IMR 4350]

You can be an NBC by birth only. There is no law on the books to make someone that was born a citizen of another country a HBC of the US. They can be a citizen but never a NBC.
Unless you know something no one else does, BO’s father was a Kenyan at the time of his birth which made him a citizen/subject of the UK. Because a father has as much rights as a mother, that made BO a citizen/subject of the UK.

[EnderWiggins]

"You can be an NBC by birth only. There is no law on the books to make someone that was born a citizen of another country a HBC of the US. They can be a citizen but never a NBC."

No law is necessary to "make" someone an NBC. As you yourself point out, NBCs are born, not made. A person born on American soil (who is not the child of a foreign diplomat or occupying army) is an NBC, no matter how many other nations also decide to grant him their citizenship.