You should not answer to a question which has no scientific value. Answering a question about race is like answering to a question about astrological sign.
It's used by the EEOC to track racial (and sexual, and disabled) equity in employment.
So what? That doesn't mean grandparent is obligated to answer the question.
And by law, you're not obligated. The contention was that such questions have no "scientific" value, when they do, insofar as employment data is useful to researchers and policymakers.