The Chinese are supplying them with the info on the backdoors they installed in the software in the electronics they sold us to put on our military hardware!
Just kidding. The Chinese are holding on to that info for the day when it’s really useful. ;^)
Your hypothesis will probably prove to be correct.
Back in the day when I was doing weapons systems design, foreign nationals were pretty much barred from obtaining the required security clearances.
But what the hell. We can get stuff for our systems MUCH cheaper if we use Chinese engineers and build it offshore.
A real sad state of affairs.