You should consider that your post has zero content other than making a personal attack, which couldn't be said for the one you're criticising.
The way I read it, is that by saying that you found it odd that people were impressed by this, it can be felt that you were implying that people impressed by this demo and code are some how backward in their knowledge or thinking. And by pointing that out, you must there for be implying your own superiority. So, bolstering self image and suggesting its ego driven fits with that.
Do you see what I mean?
You could have just said, "yeah very cool, and here is some additional info for those who are interested." But instead, you implied a negative value judgement on people who liked the demo and code. People don't like that much.
I realise that the HN readership includes a fair fraction of web developers in it's readership, so perhaps my view is in a minority. As others have said, if the link was to a technical discussion of the algorithm presented alongside a JS example implementation, it would have made more sense to me.
I do apologise if some took this as a personal slight.
HN may not need every "look at the old stuff I did in JS" post, sure. But it needs these pointless "I didn't like this" derails even less.
So what if you and a bunch of other people have been long familiar with similar stuff? When you say it "isn't that interesting" you're just saying that it isn't that interesting for _you_.
[EDIT: "When you say" -> "When you say it"]