The social nature of the lion may be more beneficial than just having someone around to groom the tough spots.
How did ALL the species do throughout the whole study?
So, the more social the carnivore, the better they were at solving the puzzle. Other studies have found that across unrelated species, brain size has more to do with the ability to problem solve than social structure, but this study seems to suggest that in species that are more closely related (the Pathera genus is estimated to have a divergence time of only 3-4 million year ago), social stucture may be a factor in how well you're able to problem solve.
Citation: Borrego N, Gaines M. Social carnivores outperform asocial carnivores on an innovative problem. Anim Behav. 2016;114:21–6.