Okay, so they didn't "change the law." It's a cool story but not a fan of clickbait titles either.
These change sets are almost impossible to use as they are, so the Council creates an official compilation of all the change sets as applied and organized by subject. This is the Code of the District of Columbia. Usually, when people think about "the law" they are thinking about the code, because that is how people interact with it.
The laws as passed by the Council cannot (and should not) be changed via pull request. Here, the useful representation of those laws, the representation used by everybody who actually interacts with the law, has been updated via PR to more perfectly reflect the underlying laws.
I mean, I'm sympathetic to your complaint. It implies something more substantive than it really means. But I also appreciate word play. (shrug)
To be fair, my own distaste for clickbait is palpable here. But I think I can suspend it in light of the importance of this article's bigger point.
I've always thought this sounded like a good idea, and to see it actually happening is pretty amazing. Here's hoping it catches on.