There's a lot of data on this subject; if you're actually interested in evaluating it as a scientific hypothesis (rather than dismissing it as heresy), this should get you started:
The study in question involves the SAT, not formal IQ tests, but the two are highly correlated. [1] You'll also see that the original claim isn't quite supported, as the poorest group of whites scored slightly worse than the richest group of blacks, but the study does broadly support the conclusion that the poorest whites outscore all but the richest blacks.
http://isteve.blogspot.com/2014/03/2008-sat-scores-by-race-b...
The study in question involves the SAT, not formal IQ tests, but the two are highly correlated. [1] You'll also see that the original claim isn't quite supported, as the poorest group of whites scored slightly worse than the richest group of blacks, but the study does broadly support the conclusion that the poorest whites outscore all but the richest blacks.
[1]: See, e.g., http://www.psychologicalscience.org/pdf/ps/Frey.pdf?origin=p.... "These studies indicate that the SAT is mainly a test of g [general intelligence]."