It's not hard to understand. People believing you are a bigot is bad, because bigotry is correlated with stupidity and ignorance, which are correlated with low

It's not hard to understand. People believing you are a bigot is bad, because bigotry is correlated with stupidity and ignorance, which are correlated with low status. He was called a bigot and he believes he is not a bigot. That's enough to cause a bit of offence.