It is true that the experiment exercises the OS, but that's only part of the point. The other part is that it uses a simple, blocking, thread-per-request model with Java 1.0 networking APIs. So this is "achieving 5M persistent connections with (essentially) 26-year-old code that's fully debuggable and observable by the platform." This stresses both the OS and the Java runtime.
So while you could achieve 5M in other ways, those ways would not only be more complex, but also not really observable/debuggable by Java platform tools.
So while you could achieve 5M in other ways, those ways would not only be more complex, but also not really observable/debuggable by Java platform tools.