What does "open source" mean in this context? I think they just mean they will publish the algorithm somehow? Are they actually releasing code under an open lic

What does "open source" mean in this context? I think they just mean they will publish the algorithm somehow? Are they actually releasing code under an open license? It may seem pedantic, but the root of my question is that when I read the article, I don't actually understand what it is they are going to do. (Also, from what I understand, there is lots of manual adjustment going on. So if they publish an algorithm for how tweets are ordered, or weighted, that would be before subjective manual adjustment anyway, making it at partly meaningless, no?)