...suggests that this may be a vague, lousy test.
So it’s a vague, lousy test that whites can pass better than black or Hispanics?
It may be a lousy test if its questions are not precise and/or if they do not measure what they are supposed to measure. Yes, it may be that some people can handle “lousy” questions better than others. There may be racial/ethnic disparities in how such questions are dealt with. More “literate” people may in fact be better at sorting through the options of even badly worded questions. You cannot know without a thorough study of the test whether it is well designed and implemented, or not.
In my own experience as a student taking standardized tests, I sometimes noticed a question that was not well worded, or for which I could tell that the test makers probably “wanted” an answer that was not really the best answer. Fortunately, that seemed to be a rare occurrence. Of course, it is not possible as the test taker to fully assess the quality of questions and answers offered, since you do not know what the official answer key may be.