They are referring to this.
Molecular Biology and Evolution, doi:10.1093/molbev/msn091
The Timing of Selection at the Human FOXP2 Gene
Graham Coop et al.
Krause et al. (2007) recently examined patterns of genetic variation at FOXP2 in two Neandertals. This gene is of particular interest because it is involved in speech and language and was previously shown to harbor the signature of recent positive selection. The authors found the same two amino-acid substitutions in Neandertals as in modern humans. Assuming that these sites were the targets of selection and no interbreeding between the two groups, they concluded that selection at FOXP2 occurred before the populations split, over 300Kya. Here, we show that the data are unlikely under this scenario but may instead be consistent with low rates of gene flow between modern humans and Neandertals. We also collect additional data and introduce a modeling framework to estimate levels of modern human contamination of the Neandertal samples. We find that, depending on the assumptions, additional control experiments may be needed to rule out contamination at FOXP2.