1. GitHub did something special or intentional in this case.
2. GitHub is running the code.
In fact, when I saw the headline, my first thought was that GitHub was using someone's library in violating of the stated license.
It's also strange that this person published their source code along with the demand that no one reproduce it anywhere.
It's like if Twitter complained about people reproducing tweets. Sure, maybe they are violating your copyright in some way, but copyright is very, very difficult to enforce on a product that can be reproduced billions of times per second across the entire world.
Especially after seeing the code itself (simple forum software that runs on PHP 5.6, which has been unsupported for 2+ years) and that the author has no intention of monetizing it, it just sounds like they were looking for a sensational headline. There seems to be no actual harm happening here.
And as others have said, this is how we'd prefer the web to work: copyright holders have less power, not more.