This is telling you that your experience is limited, not that the story is wrong. Trying to do egress filtering at scale is extremely hard for all but the most basic threats. If they open a socket to data-collector.pla.cn, yes, probably a majority of large shops would notice that within a few months but what if it's just a connection to S3/EC2, buried in the noise of all of the legitimate use of those services?
Think about how hard it is if the attacker is smart enough to bundle that into other traffic: compromise your mail server and have it respond slightly differently to some spambots, have a webserver respond to the Baidu crawler with actual data encoded in the cookies it sets knowing that the Great Firewall can pick the data up (Baidu doesn't even have to be involved – just something which gets packets somewhere they can see them), etc. If it's on a network with people, that's especially easy – is that user-agent hitting sites in China a bot or just the staffer who keeps tabs on market news for that region? (But, you may say, our user and server networks are tightly segregated! Does that apply perfectly to your terminal servers? How would you know if your web proxy started making a few extra requests?)
The mention of seeing a problem first in a Siri data center was interesting to me because those data centers probably have very consistent network activity and it'd seem like the kind of place where the defense team would have the best chance.