Its probably a deliberate exercise in color-blind casting - the practice of ignoring ethnicity and race when making casting decisions. A practice that has gone on for at least decades if not centuries in Theatre.
People don't blink twice when there is a casting decision in a Shakespeare play that casts someone of a different ethnicity than the written character, as it is an opportunity to see an actor take on one of the classic archetypal roles in literature.
It has become somewhat more common in movies and TV in recent years, the most obvious being:
Armando Ianucci the director and writer of The Personal History is quoted in Indiewire as saying:
"When I knew I was making the film, I could only think of Dev playing David,” he said. “I just thought, that’s how I must cast the whole film, cast who you think is the best person for that role."
He has also made similar (but not color-blind) choices in previous movies which go against historical 'accuracy' to create the right character, for example having Jason Isaacs (Hello Jason!) play Georgy Zhukov with a strong Yorkshire accent in The Death of Stalin
I'm going to resist commenting on whether this is a good or bad way of casting. It is just an approach to casting, and anything I say here would be personal preference. It unlocks roles that would otherwise not be available to some actors, and it downgrades the importance of a single attribute of that actor.