First, don't be so naive to think GPA as a high profile athlete is indicative of a student's abilities. At every major program I've ever heard of, these high-profile kids often have papers written for them, tutors practically doing their work and in some cases, professors seeing to it (either by choice or by pressure) they get a passing grade.
Second, that's not the case. He was admitted in that capacity because it was the only way to get him through admissions. And this isn't guesswork being done.