That's not what racism is. And don't bother digging up the 4th definition in some random online dictionary as your "proof". Dictionaries chronicle common usage, they are not the arbiters of meaning. One can understand the meaning of a word by comprehending its usage in culture and literature over the span of many decades. Once you do that you won't be able to claim that racism is "treating races differently".
To that, I say, how convenient it is that you've just turned off the critical reasoning process in your brain for just this issue. Thanks for completely ignoring the history of racial subjugation and discrimination in this country and in the world.
I suspect, however, since there's more comments than upvotes here, that a significant amount of Hacker News readers have a problem with that. I read comments like, 'oh, they should allow kids of all colors and sexes in there', and I think to myself, are you really so blind to the reality that the kids in this highly underrepresented demographic would be crowded out by other kids who already have the privilege of and exposure to computer programming.
No one is trying to prevent anyone from being programmers with Black Girls Code. They're just trying to create some comfortable space for these kids so that they can grow their computer skills as they grow up and become tech-literate adults in our ever-increasing information economy and culture that can compete on a fair playing field. That so many people here have a problem with that is highly concerning.