Yeah, Usenet was where it was at back at the turn of the millennium. Then again, I had access through a university. Access wasn’t free outside of places like that.
ISPs were spotty on coverage because even at that time, they needed at least a terabyte of storage to dedicate to it, and still not be able to cover everything that was on there. Of course, they might’ve got away with less if they decided not to carry the binaries newsgroups…
The way it worked was a lot like how Fediverse federation works now, or similarly, filesharing. It was possible to be reading a thread of messages and the older ones wouldn’t be available on your local/ISP news server because their space had been recycled for newer data.
If you were lucky, your attempt to access that message might cause your host to grab it on a future request to upstream hosts or peers, but some Usenet messages are completely lost to time because everyone purged them.
Google buying Dejanews, the largest archive of all messages, and merging it with the travesty that was (and still is) Google Groups just about killed the whole thing.
Having read some of the comments from the interviewer perspective in this thread, I am glad they got you and not one of the yahoos other interviewers got.