DEF CON goon here. Sometimes our presenters provide the link to a private GitHub repo to the press in advance of their presentation. After the presentation they make the repo public.
Might be better to encourage placeholder repository to avoid concerns from the public such as this but as long as the presenter ultimately controls the namespace it is not really at issue.
Not only are they one of their largest customers, they have physical control over the place where Microsoft and GitHub staff live and work.