I think I took that as class and race being the same - since in the 50s, they were intrinsically linked together (no black Presidents back then, as far as I can remember!).
I guess I'd argue that there's usually
a strong - if not uncomplicated - association between class and other social tensions. I mean, one of the most enduring stereotypes about Jews is that they're 'in the money'. And the numbers back that up.
At the very least I think class differences and the stereotypes associated with that magnify