Employers are probably biased towards hiring a "John Watson" over a "John Adeyemi" or even a "John Kaminski", all other things being equal. So people change their names. It's pretty common. I doubt show business is any different.
PS: UK
Who says they started with very different assumptions?
Order of preference:
1. White non-jew 2. White jew 3. Black
He changed his name so he could get by more easily as the top-ranked preference. For her, a non-jew white name would be hard to distinguish from black. She chose the name that more affirmatively promoted her above the lowest ranked spot.
I doubt either of them would disagree with the above ranking order, though.
Black Jew is rare and intriguing in a way that Black or Jew alone is not.
It's rather rich considering Trump's grandfather changed the family name from Drumpf to Trump.