I didn't claim that this was exclusively American. Though I'd have to admit that one doesn't have to be American to adopt Ameracanisms: rhotic Rs, Netflix color-grading, and copy-cat political movements are other American cultural artifacts showing up across the world due to America's dominance of the zeitgeist.
Rap verses in pop songs wasn't a spontaneously phenomenon across the globe, the origins are tracably American - but that doesn't make all rappers American.