Well, as they wrote, the mice have this slightly-different FOXP2:

> just three amino acids distinguish the human version of the FOXP2 protein from that of mice. When he engineered the FOXP2 genes of mice to produce proteins with the two human FOXP2 amino acids, it resulted in functional differences in brain areas critical for carrying out fine motor tasks and controlling muscle movements, as well as altered function in regions involved in sending and receiving reward signals. […] mice with human FOXP2 learned faster than regular mice.

I found it quite funny that there's been all these news reports on FOXP2 being "the language gene", and then someone goes ahead and makes mice with human FOXP2. Unfortunately the mice did not learn to speak :-)