I'm highly doubtful this is a "caching issue". This sounds like a problem on Steam's end.
For starters, you don't cache everything at the CDN and information that's supposed to be encrypted is still encrypted. If Steam is caching all of this at Akamai they're idiots and it's still on them.
So even if it is "caching problem" it means that Stema has been caching unencrypted, raw account info at Akamai, though again, I'm very doubtful this is due to an issue there.
What seems more likely is that someone made an oopsie with the customer information database (drop a few key rows and suddenly info is showing up where it shouldn't have) or a straight-up hack.
Others are free to weigh in on this. I work in the webhosting industry and deal with CDNs on a fairly regular basis. Our company uses Akamai as well.