It appears the family of the young man in the article made use of a number of familiar HG+ resources, including Duke TIP and Davidson.
The critical change that prevents any other students from following the same path is that Harvard Extension now requires a high school diploma prior to admission to the baccalaureate program, but not to taking courses. Hypothetically, I suppose one could take nearly all of the courses required for the BA, while completing credits for high school graduation (simplest would be to take the HE credits as dual enrollment), take a HS diploma prior to registering for the spring semester, apply for admission at that point, and then complete the BA, which would have HS graduation occurring about six months or more prior to college graduation. If that matters to anyone!
Dual enrollment is probably the most important contributor toward the number of young students completing some level of college degree at the same time as a high school diploma (AA/HS, BA/HS, etc.)
