It's not certain exactly what would prompt an escalation, although there are multiple possible factors. China and the US have been engaged in a trade war in recent months. And while it happened too recently to play into Joyce's remarks, the arrest of Huawei's CFO hasn't exactly helped diplomatic relations.
While hard facts supporting the charges are hard to find, that's not slowing down the rhetoric. Reuters sources said American prosecutors are close to charging Chinese residents for participating in a digital spying campaign that targeted tech providers and their customers. Tonight the New York Times reported that preliminary results of an investigation into the Marriott/Starwood hacking incident suggests it was part of a Chinese intelligence operation. China has routinely denied conducting any hacking attempts, and Chinese Ministry of Foreign Affairs spokesman Geng Shuang said to the NYT that: "China firmly opposes all forms of cyberattack and cracks down on it in accordance with the law."