I wasn't talking about "verbal ability" (which, to the extent that can be found out in ten minutes, correlates more with where someone grew up than with IQ), but about what they say, e.g. their reaction to finding out that I'm a physics student (though for this particular example there are lots of confounding factors), or what kinds of activities they enjoy.
If you're able to drive the conversation like that, you can get information about IQ, and that information may have a larger impact than race. But to "screen off" evidence means making that evidence conditionally independent- once you knew their level of interest in physics, race would give you no information about their IQ. That isn't the case.
Imagine that all races have Gaussian IQ distributions with the same standard deviation, but different means, and consider just the population of people whose IQs are above 132 ('geniuses' for this comment)...
Here's the new thread for posting quotes, with the usual rules: