can you please explain this question more: why is tateh's attitude toward his Black customers ironic?

Blacks and Jews in Suffolk were equally discriminated against. Tateh was a victim of prejudice, and yet ironically, he treated his black customers the same way that he was treated. You would think that Tateh would understand prejudice and treat his black customers with respect because of his own experience. Unfortunately, he was just as racist as the people who mistreated him.