That's a really great point, and shows a deep understanding of how consistently humorless HN users are! If you want, I can show several more examples of people knee-jerk downvoting things that are actually pretty funny.
There's always been a general pushback on HN against turning threads into a series of quippy oneliners. It tends toward having a serious discussion about a topic, rather than farming low-effort humour for upvotes. I consider this a good thing, as there are plenty of other places where that is rewarded.
Yeah it seems harmless in isolation, but I'm pretty sure that lacking a norm against it it is one of the ways you end up with Reddit. And because HN doesn't have an actual anti-humour rule, in the best case it lets the funnier and more creative stuff through while punishing the obvious one-liners and boilerplate jokes that everyone would be clamouring to make first on a Reddit thread. (I don't want to be rude, but the thing where someone writes stereotypical AI speak in an ironic context has been done a billion times and doesn't need to be done again, unless it comes with an interesting twist or unusually sharp execution.)
I agree though from my experience on HN people tend to upvote these funny quips instead of abstaining. Yet generally when I write something meaningful I get meaningful replies in return sans upvotes and I treasure those much more.
I still cling on to the quaint idea that "upvote" means "adds meaningfully and coherently to the discussion", while "downvote" means the opposite. So not "I agree with this" or "that made me chuckle" but rather "this enhances the conversation" - and especially if it's a well written argument I disagree with because that might make me learn or rethink my position. Humour in a well argued point is very welcome, of course.
Wish and reality aren't in alignment here but some places like HN or /r/AskHistorians are my refuges.