Branch names can have slashes but not repo names, and github seems to render any activity related to branches like so:
![githubbranchwithslash](https://f.cloud.github.com/assets/98299/1048981/fceb323a-1097-11e3-8eb9-2d4a276d5542.png)

Thus, the current method of extracting the Username/RepoName works as expected.