US charges two Chinese spies for a global hacking that targeted Covid research

> Mandiant, the incident response division of security firm FireEye, said it has tracked the hackers since 2013 and the tactics, techniques and procedures used by the hackers is “consistent” with its findings

Can anyone from infosec chime in? I'd love to know how pattern recognition works in figuring out specific actors, since I don't have a good idea what "techniques" here means. Is it the malware used, the attack vectors, or something else?

This link had a GDPR-wall that had no opt-out choice, better one: https://www.bbc.co.uk/news/world-us-canada-53493028

I think it's kind of hard to defend keeping covid-19 vaccine research findings as proprietary in the current times, I hope that's not what this is about. (charge is "Prosecutors said the two men spied on a Massachusetts biotech firm in January which was known to be researching possible cures for Covid-19")