I think wolfman had it right. It's hard to believe "Nature" would stupe this low. I'm more inclined to agree with Robert Wayne Phd who was also quoted in the article.
From his website: http://www2.fiu.edu/~milesk/Genetics.htm
DNA: Wolves & Dogs
Mitochondrial DNA analysis, rather than nDNA analysis, is widely used to study populations of many animal species (including canids) because of its advantage over nDNA in that it does not recombine with other DNA as nuclear DNA does. The only way to conclusively determine (thru mtDNA) if a canid contains wolf content would be the presence of mtDNA restriction fragments specific to wolves. This is the root of the whole problem scientists are encountering when trying to differentiate between wolves and dogs. They are just too closely related, which is what led to the Society of Mammalogists and the Smithsonian Institution's taxonomical reclassification of dogs ( Canis lupus familiaris) as a subspecies of wolf (Canis lupus) in 1993 .
Many people erroneously believe that wolves and dogs are distinctly separate, one being 'black' and the other being 'white'. Throw in the wolfdog, and these same individuals see a completely different color: blue, green, purple, etc. However, Monty Sloan of Wolf Park put it simply: "there is no black and white in this issue, only shades of agouti gray."