From the article: '... the [Fourth Circuit] held that because UMW had the "technical capacity to control the means by which the harassing and threatening messa

From the article: '... the [Fourth Circuit] held that because UMW had the "technical capacity to control the means by which the harassing and threatening messages were transmitted" (that is, the ability to block campus network access to Yik Yak altogether) ... UMW had substantial control and thus could be liable for the harassment.' So you're right that the court didn't explicitly require the university to do anything, just as courts don't require that people refrain from committing murder, but if you murder someone, a court will likely lead to you being punished. With the threat of being potentially held liable for harassment, there is at least a strong motivation (if not a "requirement" as such) for the university to "control the means by which the harassing and threatening messages were transmitted", especially if that is the simplest or cheapest way of avoiding liability. I suppose that if that happened, and if my theory about the First Amendment is correct, then affected students could bring their own case and demand a different resolution to the issue in this article.