Cybersecurity is a cat and mouse game, nobody made their methods public, on any side. How do we know that you aren't from Chinese intelligence who is trying to figure out why they could trace back to the Chinese hackers in this case?

If Mandiant said they caught a Chinese hacker red handed by tracing the connection to his house in Beijing, and they were able to record his keystrokes, would you believe them?

When Kapersky said they discovered zero days by US intelligence, they gave no evidence either:

[FSB] goes on to claim without evidence that the attacks amount to a plot between Apple and the NSA to build a powerful surveillance infrastructure to snoop on those with ties to Russia.

https://www.darkreading.com/endpoint-security/apple-zero-day...