He was taking money from the department of energy for research while collaborating with Chinese universities and did not disclose this and lied to investigators about it.
There is no ban on collaborating with Chinese universities in the US. There are restrictions for some type of research (that actually extend to the other countries as well).
It's the "Martha Stewart" lesson. It may be that you have done nothing wrong. The government may stop by and ask you questions anyways. If you lie during those questions you have committed a felony.
Do NOT speak without a lawyer. In particular if you have anything worth losing. Which is more or less everyone.
[1] https://cen.acs.org/research-integrity/misconduct/Court-over...
> At issue in the new ruling, issued 11 July, is whether Tao’s lack of disclosure about his affiliation with Fuzhou University in China affected federal agency funding decisions. The Denver appeals court agreed 2-1 that it was irrelevant because Tao had no grant proposals pending before those two agencies in question – the US Department of Energy and National Science Foundation – at the time he made his affiliation statement.