The first part and the second part are kinda strongly contradictory though? Clearly someone in America did sell something at some point, we just don't know what it was since they didn't get caught.Ask yourselves how come no American has ever sold US nuclear secrets to China (on public record) and yet it is clear on two occasions this decade where Chinese nationals have sold China's nuclear arsenal related secrets to the US. China no doubt has strong intelligence gathering in the US. The US recognises this and China has in the past revealed it held high level details on US warhead configurations.
While China has advantages that can translate to stronger SIGINT, SIGINT is also a little overrated, a lot of spying comes from good old human intelligence.That is more likely from effective spying rather than some American General just handing over documents to the Chinese.
If China had got US' high level 5th gen, nuke intel purely through signal intelligence without setting a foot on US soil, that's a ridiculous level of tech overmatch.
I think rather there are a lot of Chinese spies, and unlike what racist US thinks, these spies are almost all whiteys. Because it would be obvious if they're ethnic Chinese...
US has some problems even properly auditing the Pentagon's budget, it's not so unbelievable that they have a real spying problem and are unable to catch many of them.