I means the CCP have access to diplomatically sensitive material, and it sounds like the infiltration via email has gone farther than just this ambassador, all the way into the top levels of the State Dept.
And if the State Dept got hacked by this, for who knows how long, then the possibility they pushed out farther than just the State Dept has to be considered, and with the US track record of protecting ourselves from the CCP, expecting the CCP to have anything in the US gov that isn't air gapped or only on paper is hardly unreasonable.
So while they may not have some of the super secret sauce, like the launch codes and shit for the nuclear triad missions, they probably have enough to help them engage in non-kinetic attacks,or just more accurate/skilled influence ops, on the US populace and economy.