Copyright doesn't protect your brand name. Trademark does.
Trademark doesn't give you blanket protection that stops every other person on earth from using your trademarked term. What you get instead is a highly context-specific protection. A trademark protects the use of your trademarked term in a specific service/goods segment. When you see trademarks like Ford, Apple, or Google, that seem to have unbelievably wide protection for their trademarks, that seems to span across wide spans of the market, that is because their brands are very well known, and because the use of their brand by a third-party could create a confusion in the consumer as to the origin of the goods/services.
If there is no confusion in the minds of consumers as to the origin of a message/good/service, then the use of a trademarked term is not restricted.
In this case, this guy is virtually unknown. Not a single person thinks he is the one running this conference. Its clear the conference is being run by other people.
You cannot claim an absolute property right to a silly sequence of words just because you think you said it first, and because you made a domain.
Yes, the domain and the twitter handle should be yours by right of first occupation. But nothing more.
edit: changed "absolute nobody" to "virtually unknown" to address rudeness concerns.
edit: with regards to the charge of rudeness leveled against the conference organizers: In a world literally flooded by brands and names, name collision is not rudeness, it is almost inevitable.