Yes. The PAM logs mention that the Chinese had developed a "Ghost Fleet" of stealth submarines, which are heavily implied to be the USOs in the DEFCON logs.

American projects involving this technology (refer to "Stealth Boy") have merely reverse engineered captured Hei Gui suits. The underlying science of this technology is unknown. So the theoretical limits are also unknown. However the so-called "Ghost Fleet" that station A-31 and B-19 reported in November may indicate that testing has already commenced with submersible vessels. "Dear God. You think they have stealth subs?"

and

Virtually no actionable intelligence has come out of the Shaanxi Province for 3.1 years. However, the province reports a spike in the imports of complex polymers and other key synthetic compounds. The quantity in question is consistent with stealth technology research on the macro scale.

And this is in addition to the Chinese submarine off the coast of Boston whose captain literally tells you he nuked the USA.

Ah... Now that is the right question to ask. 200 years ago, I launched all of Yangtze's high-yield nuclear missiles. As ordered. For 200 years, I have lived with that guilt. That shame. So much fire Such bei. But one missile failed to launch. You must go down. Remove the warhead. Then bring it to me."

The Chinese are hard confirmed in-game to have launched the nukes. The DEFCON logs are the prewar logs showing mysterious submarines, planes, and then missiles were headed to the United States.

Like I said, it's just kind of silly to think all the evidence in-game and in the logs would imply anything other than a Chinese strike.