Not only were you wrong in this case, you would be wrong in most cases. Most blacks may vote democrat, but they aren't Marxists. Most don't have the political sophistication or awareness to even know what Marxism is.
Of course they don't know that the view that their predicament is solely the result of the struggle between racial/socio-economic groups for power and control is a MArxist viewpoint, but they still believe it.
I'd say 95% of American blacks believe wholeheartedly that critical race theory is the most apt explanation of history.