I think that may be the first time I've seen licensing drama over something as minor as adding another author to the copyright list.

Pretty sure those are completely standard for major changes in maintainers/hostile forks/acknowledging major contributors. I've seen a lot of abandoned MIT/BSD projects add a new line for forks/maintainers being active again in order to acknowledge that the project is currently being headed by someone else.

From my "I am not a lawyer" view, Kludex is basically correct, although I suppose to do it "properly", he might need to just duplicate the license text in order to make it clear both contributors licensed under BSD 3-clause. Probably unnecessary though, given it's not a license switch (you see that style more for ie. switching from MIT to BSD or from MIT/BSD to GPL, since that's a more substantial change); the intent of the license remains the same regardless and it's hard to imagine anyone would get confused.

I suspect (given the hammering on it in responses), that Kludex asking ChatGPT if it was correct is what actually pissed off the original developer, rather than the addition of Kludex to the list in and of itself.