You are describing domains, and neither the article nor its title suggested the discovery of a new domain. There's no technical reason I'm aware of for "branch"

You are describing domains, and neither the article nor its title suggested the discovery of a new domain. There's no technical reason I'm aware of for "branch" to be restriced to describing domains of life. This case appears to demonstrate a new phylum, which is two steps below domain, so it's still significant in terms of classification. The fact that the organisms resemble some others we thought died out long ago is also important for evolutionary biology.