SAT Inferences Question

Andrea Sommese, Andrea Temesi, and team investigated head-tilting behavior in a group of forty dogs, which included thirty-four typical dogs from five different breeds (including Benhur, a kelpie) and six dogs that had previously demonstrated giftedness at learning words, all of which were border collies. The researchers recorded the dogs' head-tilting behavior in response to requests to fetch a toy that had been introduced early in the study. They found that all six gifted dogs tilted their heads at least some of the time when asked to retrieve the toy by name, while the typical dogs almost never tilted their heads. After reviewing the study, a student concludes that a tendency to tilt their heads is a characteristic trait of all border collies. Which finding from the study, if true, would most directly challenge the student's conclusion?