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).
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.
"In computer science, concurrency is a property of systems in which several computations are executing simultaneously, and potentially interacting with each other. The computations may be executing on multiple cores in the same chip, preemptively time-shared threads on the same processor, or executed on physically separated processors."
A multi-threaded program running on a single core system has only one path executed at any given time, but we still call it a concurrent program.
There is no such thing for node, unless you use a compiled addon. Node has no blocking networking facilities.