The brown acid?
What I take from that is, assuming it’s accuracy, at this period in time it was commonplace among peers to use personal email addresses - I mean, how do you get the British PM’s, the German Chancellor, even Putin’s personal email addresses unless you’re all swapping contacts at the G20 or whatever.
And why? Was it just more relaxed/naive or did some prefer to avoid the scrutiny of the NSA or equiv.
And it also looks like it was normal at State, as well. People knocking off emails to each other on Yahoo or whatever.
So - according to Mr UN Bullshitter - it was a culture … as mentioned, it might be because people were still working emerging technology, but their might also be an issue of avoiding ‘the watcher’.
Frankly, they’re all better off on encripted-both-ends WhatsApp now. I hope they have at least that much sense 
I recall the insane contortions the field-level USAF was going through in the 1980s dealing with the advent of pre-PCs and then the *en masse *deployment of PCs, both ones folks brought in from home and officially supplied ones.
What information could be stored where and how was all over the map. Some authorities believed no personally owned PCs were permitted, period. But the same info could be safely processed on a plain ordinary Dell or IBM that came through the GSA supply system.
Others drew lines in the sand at various levels and quantities of classification. e.g. A personnel roster for one squadron was OK. Put two squadrons’s rosters on the same machine and you’ve created “implicitly classified” info which was verboten.
The NSA/COMSEC folks’ view was simple: “Stop the train; we want to get off”. IOW, we want to prevent 100% of any computers being used in the field for any purpose whatsoever until they’re all provably secure to Top Secret over their entire lifespan. Including cradle to grave tracking for every component part, diskette, and paper or electronic transmission that went in or out of the machine.
The rank and file mid-level officers & senior enlisted just wanted to be able to word-process their unclassified memos in peace and use 1-2-3 to track their beans, bodies, and bullets.
It was regulatory and compliance chaos. And this was before the internet and the explosion of email as a business process tool.
Well, at least we know that AOL accounts are completely secure, right? 
Many years ago I noted that my then-employer, a financial regulator, was exchanging official market-sensitive information with firms who were using Hotmail accounts (note: the firms were using Hotmail, not us; some of the companies were relatively small). I suggested to a key manager that perhaps this was not particularly good practice considering the sensitivity of such information. Shortly thereafter the memo went out that no formal comms should be sent to firms via third-party email servers.
As LSLGuy noted, it takes a while to adjust to the changing landscape of electronic communications and its risks vs its rewards. If you’re lucky, nothing goes wrong before you get caught up. If you’re not, well… sucks to be you.