I agree that a more fitting line would have been, "I show how to build a modern C++ high-performance, asynchronous echo server using Facebook's Wangle (which comes out to be only 48 lines of code).

However the TITLE OF THE ARTICLE is "Writing modern C++ servers using Wangle." Furthermore, the author states that he's using that framework almost immediately after the statement you quoted, so I really see nothing to complain about. It would be more of an issue if the author led with a huge introductory paragraph or click-baity title that failed to mention the library she or he is using.

Knowing how many lines it took for the author to implement the server in the Wangle framework is very relevant to the reader.