On their FAQ page they state that their app is 'public source'. I assume that is so you (or presumably your organization) can audit (rather than debug) it if necessary.
I've not tried it, but they also suggest you can compile your own binaries from that source to get around the untrusted binary problem.
IANAL either but I agree, that is a statement of copyright which is not unusual, but there is no licence and therefore we have no right to copy & use it.
> If you set your pages and repositories to be viewed publicly, you grant each User of GitHub a nonexclusive, worldwide license to use, display, and perform Your Content through the GitHub Service and to reproduce Your Content solely on GitHub as permitted through GitHub's functionality (for example, through forking).
We are granted a license to use it on GitHub by the GitHub ToS.
I've not tried it, but they also suggest you can compile your own binaries from that source to get around the untrusted binary problem.