Nobody called the Japanese stupid. You chose to interpret it that way. Actually, I understand how it could feel that way, and I empathize. But take a look again:
https://news.ycombinator.com/item?id=22730110. It didn't say that. What it did do was repeat an internet cliché [1] in a lazy way. That made it an unsubstantive comment, and an unsubstantive comment on an inflammatory topic is basically always flamebait (as I pointed out to another user earlier today:
https://news.ycombinator.com/item?id=22739350).
You've unfortunately been posting to HN quite a bit in the flamewar style. Would you please stop doing that? I realize that these topics are sensitive and hit sore spots all too easily. That's one reason the site guidelines include: "Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith." It isn't easy, but it's necessary that we all do it, because otherwise we just end up fighting with each other. Fighting each other feels urgent, but is not interesting, and the purpose of HN is to be an intellectually interesting place on the internet, if possible. This requires that we sort of resist the worst interpretations of each other's words, because they're so often vulnerable to misunderstanding.
By the way, in case you're not familiar with so-called Hanlon's Razor [1], it's not primarily about stupidity. It's really a way of saying that most human outcomes are not the result of malice. So in a way, that post was a (weak and unclear) defense of the Japanese institutions and reports that were being discussed above—a way of arguing that they weren't conscious bad action. The word 'stupidity' appears in that proverb partly out of ironic humor which is typical of the internet subculture that produced it, since it's ironic to defend someone against the charge of malice by making the charge of stupidity instead. It's not intended as the deep insult that the word 'stupidity' would imply in many cultural contexts. If you already know this, I apologize.
There is an additional level also. The word 'stupidity' in that proverb would not normally be a national or racial slur. It usually refers to the 'stupidity' of large institutions, which tend to produce inefficient or inadequate results even when the individuals who make up the institution are doing their best—or to the 'stupidity' of bureaucratic functionaries, who hacker-type people tend to feel superior to and smarter than. If you look at https://news.ycombinator.com/item?id=22556236, you'll see exactly the same argument applied to Spain's Covid-19 response. If anyone is being criticized as stupid in those comments, it's not peoples like the Spanish or the Japanese, it's mid-level government officials everywhere. Whether that's fair or not, we can leave as a separate question.
[1] https://en.wikipedia.org/wiki/Hanlon%27s_razor