Years before BTS broke the seal on K-pop in America, Teddy Riley saw the vision. The R&B trailblazer, whose production and songwriting pioneered new jack swing in the 1980s and ’90s, turned an ear to Seoul in the late 2000s, producing for K-pop groups like f(x), EXO and Girls’ Generation. The marriage was arguably overdue: A generation earlier, Riley’s signature sounds had been all over the single most important breakthrough in K-pop history, the 1992 smash “Nan Arayo (I Know)” by Seo Taiji and the Boys, the first crew to not only experiment with Western influence but mimic its artistry and fashion wholesale. And so, when Riley arrived to service the now fully built pop industry that had taken shape in South Korea thanks to the “Nan Arayo” revolution, the producer was well aware of his role in the process. “They didn’t have no shame in their game. ‘We want the American culture,’ ” …