I guess it makes sense that for stock figures or background characters in an adventure story of the time, he'd stick in something expected. It's heartening that his own sense of character and storycraft, when engaged, doesn't require that, and really, from what you describe, there are lots of really well-portrayed nonwhite characters. Too bad white supremacy meant filling in the background with caricatures...

ETA: And thanks very much for this thoughtful comment--it's fascinating to hear these snippets about the other stories.