Racist Poll on Racism

I don't get it. A survey was conducted to determine how blacks are perceived by whites. Using a framework of "How well does each of these words describe blacks?", the survey throws out words like "hardworking" and "friendly."

How do they get away with this? They're asking people to make a sweeping judgment about an entire population of diverse individuals. I understand that it's trying to measure bias or prejudice, but isn't this survey inherently so?

Would you describe all whites as "hardworking" or "lazy"? Of course not - everyone is going to be different and the variety is overwhelming. How is this premise even valid? Am I overreacting?