Old Money from another race. Hmmm They came to America from another country it is really isn't that hard. A wealthy Moor came to America back in the 1600 or 1700s . But even without thinking that way anyone in the Wanye line marries a Black,Indian,or Hispanic Woman. It really isn't that hard to imagine but yes old money in the US especially is majority white but to get that different perspective you have to be able to see the world in a different way. It fits easily into his mythos Bruce grandpa married a Black woman.It is as really just as simple as that.
This topic is not about plausibility because what is the likelihood ship landing in the right place not being seen for a kind family take in alien kid and the kid being able to blend in? The person writing can make things more plausible .The topic as I see it is really about how some fanbase are unable or unwilling to see character as another color but they have ability to see Egyptians,Indians or Asians played by white people and not disrupt their experience but reverse is too jarring to happen. For years this type of change going the other way never stop people enjoy of movie or tv show.
Are they going to change Superman race? No. No main major high profile character has been "racebent" they highest profile characters have been Johnny Storm or Wally West. If they ever decided to "change" Superman he would probably be part white like Jason Momoa Aquaman or Zendaya MJ. Which always leaves people complaining with not quite enough ammo to make a point because someone Dean Cain is part Asian, Tyler Hoechlin is part Native American did it matter? It didn't stop them from being good Supermen. Here is the funny thing once you say Cain is Asian or Hoechlin is Native American you can see it and they got the job not because they are white they got because look enough like Superman. Which changes up what is real being look for which is Black hair, Muscular build, Strong jawline and some degree of caucasian skin color.