The lesson:
SC Democrat primary voters are mostly black
Therefore, SC doesn’t matter
Trump has 30+ % of black voters nationally
Reportedly 60% of the Democrats in South Carolina are black. (I don’t know what the percentage was of those who actually voted in the primary.) If Biden got 60% of the black vote and a little less than half of the overall vote, it suggests he had about as much of the white vote as one or two other candidates...possibly more but not by much.