You are correct. It is not related to Stack Overflow. As a proxy between the user and Stack Overflow, they are technically using Stack Overflow content and... sort of... attributing properly (since the content appears to already be on Stack Overflow...). But that point is irrelevant: we also have a rule that states that other sites using our content may not copy the look and feel of Stack Overflow (or another network site) to confound people into thinking they're on SO.
While we can indeed do nothing about their domain name, as BoltClock said, we do have several tools in our legal toolbox we can swing at the content of their site. Which is the content of our site. Through a proxy.
So, the proxy issue is complicated, but you can consider my attention brought! (I am the SE employee who handles the initial "please cease and desist, good sir or madam" notices to try to crack down on this kind of behavior.)