Those must have been the personal e-mail accounts of the military members not their military ones those are .mils and are lastnamefirstnamerank@base orcommand.mil I doubt they'd hack those so easily.
Still how did these Chinese hackers know that they where hacking the accounts of military members?
A good lesson in why OPSEC is so important(loose lips sink ships).I never spoke of military duties off base in any detail nor over the phone or in e-mails and I still don't say very much about my old job not any technical or ops details anyway.I have an old friend who is in military intelligence security he hates sites like Facebook with a passion because of OPSEC loopholes from members of Facebook who are the military and give out details even what seems minor is useful to someone who knows what to look for.