The plausible interpretation is that the commenter got excited about screen readers because they unexpectedly connected to something he was already interested in, and it made him curious. Not only is that a perfectly decent thing, it's an example of the curious conversation that HN exists for.
Meanwhile, snarking and putting down other users, which unfortunately are what you did, are examples of what HN very much does not exist for.
It's really easy to interpret other people's internet comments in ways that add things that weren't necessarily there. We have only tiny blobs of text to go by. We don't know each other, and we don't even have the cues that come from voice, body language, and the like. As I read the GP comment, it seems to me that it was you who introduced the notions that it was somehow about the commenter puffing himself up, or that he was somehow lacking in compassion towards the original poster.
In a thread of 200 comments, there will inevitably be rivulets of conversation that aren't about the main theme. Such tangents are only bad if they're somehow generic and predictable. This one was interesting, still very much in the orbit of the main topic, and I really don't think there was any meanness in it. I'm pretty trained to pattern-match meanness after years of trying to get people to be kind to each other on HN, and I'm afraid it was your comment that was the mean one.