Rare South Carolina Primary Poll has Suspect Demographics

With so few current polls in South Carolina, looking in detail at these polls is even more important.

The demographic breakdown in the YouGov/CBS poll looks suspect.

The % of Democratic pollees that are black is 62.5%. In 2008 when there was a black candidate running it was only 55%. The racial composition of the state hasn't changed since 2008 so why would a race feature two white candidates have a surge in black voters? if anything, one would expect the black vote to be less than 2008.

Even if the demographics were like the extraordinary 2008 primary, the 73% of black voters for Clinton would suggest a 6 point reduction in Clinton's lead. A 56/43 vote split. More likely the demographics are not so favorable as 2008, meaning an even closer race.