Mate I think people are just kinda lazy and don't really care that much about privacy relative to ease of use and the presence of people they're interested in.
The point of the article is to appeal to people's hatred of Meta (which is well-earned, admittedly), not to actually say anything meaningful.
Having observed conversations about Threads here and on Lemmy, it's a pretty dependable tactic. I completely understand not wanting to associate with Meta and not trusting their intentions, but there are plenty of things to criticize them for without trying to whip up a fury over what's objectively not problematic. But this is the internet and people like being in a fury, so whip one up they will.
I think there's something to be said for it being public. If someone's downvoting all of your content for no reason without engaging with it, that's obviously not someone worth your time and it may be a decent idea to just block them. I could also imagine some communities making it explicitly against the rules to downvote constructive comments for no reason, for instance.
At any rate, my understanding is that the actions must be at least publicly accessible in order for federation to work, so the only thing that Kbin could do is simply not openly display that data. Perhaps making it less accessible would reduce the temptation to look, but it'll always be available to anyone who truly wants to see.
I'm not sure how much you know about networking or HTTP, but from the evidence posted, this very much is not the kind of thing that just accidentally happens.