I certainly don't like to go around spouting nonsense, so I spent some time looking for formal definitions of concurrency. I wasn't able to find any support for the description you provided, though. Do you have a source?
FWIW, Wikipedia seems to believe that "concurrency is a property of systems in which several computations are executing simultaneously, and potentially interacting with each other".
Regardless, sorry if sloppy (or poorly defined) terminology obscured my point.
I hope this isn't too pedantic, but I wish the author would stay away from calling Node "concurrent". The whole point of Node is that it's asynchronous but not concurrent: there is a single thread of execution for your whole program, which is what lets you ignore locking, etc.
In fact, when you program for Node it's really important to keep this in mind, since (contrary to another statement from the article) not all libraries are asynchronous. If you select a synchronous db driver or write a long-running loop, it will block the rest of your program.
In general, though, I thought it was a good piece. I'm sure many heads have exploded on first introduction to node (and JS in general).