What is he misunderstanding? There's nothing in the post mentioning copyright or suggesting the author thinks he has a legal case. He just thinks New Relic are being jerks.
In a world literally flooded by brands and names, name collision is not rudeness, it is almost inevitable.
Aside from that - well, it was a pretty rude move, particularly in that they didn't bother to acknowledge him when he talked to them (albeit over twitter) before ranting about it.
I don't think there's a question that the conference can do this legally, but they're still being ass-hats by ignoring it (and getting his twitter account suspended).
I just don't think people have to abandon a cool name just because someone somewhere registered a domain or has a twitter handle with the same name.
Ideally you make up a new word for your new enterprise. But it ends up being harder than you think if you are trying to name something with an identifier that means something in a domain. Anyone that has to name a new product or company can attest to this.