Last year, China’s tech stocks cratered. This year, America’s are following suit. But their selloffs have very different drivers, and therein lies a potential inflection point in the emerging competition between the two countries. The Nasdaq correction is the natural consequence of speculative froth that allowed numerous unprofitable companies to go public and many established companies to achieve nosebleed valuations. By contrast, China’s selloff was the result of a deliberate policy by the ruling Communist Party to rein in its freewheeling entrepreneurial class and reorder its investment priorities. The distinction matters because, thus far, the two tech sectors have had...