The comment you quote is trying to explain that when you use any of the
async versions of i/o APIs within .NET, the .NET Framework is using IOCP
in its implementation.
In other words, as long as you are using the async versions of the i/o
APIs (e.g. Stream.BeginRead(), Socket.BeginSend(), etc.), you get the
use of IOCP for free. This includes the use of the thread pool to
process the i/o (in fact, the main System.Threading.ThreadPool class in
.NET includes support for both non-i/o and IOCP threads???they are
maintained in separate pools, but the same class handles both).