Achieving high test scores is not the same thing as teaching to the test so I wouldn't assume that is the case, especially if the student population is gifted and the school does lots of special interest events (pulling out students for extra work and training and growth).
My sister's kids go to a school like this and they are thriving. They limit each child to one activity, usually music lessons, more because of the large family size and desire for family relaxing/down time then the rigorous schedule. They tend to host play dates rather than go out for them because it is easier toschedule. They are very, very active in their church as well. The only other rule is that the kids go to a limited number of birthday parties because it gets overwhelming quickly. She is never concerned about friends/socialization as much as letting all the kids have a chance to play together and be together as a family.