I've used both at length, and still use Usenet to this day. Besides reddit being centralized, how are they dissimilar? Is it really that bad if an analogy for a readership that likely have no clue what Usenet is?
Usenet: it's on you to create filters and mute threads that you don't want to see. Everyone is their own moderator. (Pretty much exactly in the way that you're the moderator of your own email inbox, smart recipient-side filtering and DNSRBLs notwithstanding.)
It seems like a small difference, but I feel like it's actually responsible for large social differences in the resulting communities.
In a Usenet group (or, equivalently, an unmoderated email list), the spam and flames are visible to everyone, and everyone is forced to engage in at least a bit of the work of moderation—even if it's just to copy and paste a blacklist from an FAQ message into their NNTP client's config. This, IMHO, makes people less likely to overreact to negative/offtopic/trolling/spam posts—they're inured to them, in about the same sense that an immune system that frequently interacts with real threats is less likely to get an auto-immune disease; or about the same way that people who live in the projects are less likely than people in gated communities to call the police just because someone they don't know is walking down the street.
I should probably add that I'm saying this as a fan of and avid user of reddit. I'm unhappy about what we lost as Usenet wound down, not complaining about reddit.
While that is true, usenet also has moderated[1] groups (e.g., misc.legal.moderated).
My cringe wasn't due to a bad analogy. I was cringing because I remember what usenet was like once, and the last time I spent much time there, it had lost so much of what made it good that, yes, comparing newsgroups to subreddits is essentially on point, now.
I cringed because the analogy is on target and I don't like that as much as I liked usenet before. Comparing it to reddit gives a pretty good picture of late stage usenet for people who didn't experience it. At one time (I think including the time period this article is covering) there was more to it than that, though.
Conflating Usenet with reddit is like conflating the Internet with AOL.
I'd say it's bad for the readership because it gives them wrong information. I always feel it's better to have no analogy than a bad one.