He collaborated with war Hawks in the USA like Bolton and Pompeo as part of his campaign as a British national to fight against the return of Hong Kong to the governance of China, spread anti-chinese propaganda, and politically organizing against the state.

That’s all that’s needed. If a British national who lived in California and built up relationships with Russian and Iranian leaders was organizing politically to have California secede from the USA you can be damned sure that person would be in prison.