I think that's false. African Americans are about 20% European in ancestry if memory serves. Of course if eugenic selection did its work, some high IQ alleles may have escaped the "neutral" baggage from the Native American and European gene pool.

Lynn's exact numbers, while spot on the general pattern, have been criticized by others. There are a some studies that point to an actual IQ (that try to estimate the effects of things like people being unused to using a pencil or solving the test in a nonnative lanugage) nearer to that of 75 and a handful even something as high as 80.

Regression to the mean of the children of African immigrants in Europe, points to a 80ish IQ once environmental advantages kick in.