If I'm reading the article correctly, the author is saying that with parallelism, you can perform independent operations in parallel (like sorting both halves of a quicksort), whereas concurrency as people think about it deals more with parallel operations on a shared state?
Parallelism often implies that the tasks are working towards the same goal together, like dividing-up the workload among sibling processors. This is purely for performance.
Concurrency is simply the introduction of non-determinsm, like having a thread run a task in the background. Concurrency can be used to make a networked GUI application more responsive to the end user, even if there is no performance benefit.
