The "really clever design" as noted by simonw was called "nothing fancy at all" by ComputerGuru, and that haveibeenpwned's API design "hasn’t done anything remotely ingenious", this is what made the comment pretentious. (in this case it doesn't matter wether he is or not factually correct)
The reply could very well be interpreted as "You think that Kk-Anonymity is fancy? How primitive of you. This way is the natural way of doing that thing and I would know because I'm the smartest person in the room. Oh by the way I dislike people who are pretentious."
I’m sorry if that’s how you understood it. This is not about the HIBP api but rather the braggadocio in Cloudflare’s post. I meant “they are purposely obscuring how obvious and intuitive their solution is behind all this math so they can seem extra smart, and it’s a shame because it would have been a better and more actually educative post if it just said ‘we did something very obvious and maybe you can just as easily do the same to your own data without being a math geek and it’s no big deal at all that we did, but here’s how we did it anyway.’”
Consider the possibility that those of us who found it pretentious aren't lying, and that you not seeing it is perhaps more related to how you personally see things.
Now you're mis-representing my comment, I didn't anywhere discuss whether or not it was pretentious, I just pointed out that the comment was factually incorrect.
The reply could very well be interpreted as "You think that Kk-Anonymity is fancy? How primitive of you. This way is the natural way of doing that thing and I would know because I'm the smartest person in the room. Oh by the way I dislike people who are pretentious."