That doesn't make sense. For example, GPLv3 allows anyone to redistribute the software's source code if the license is intact:
> You may convey verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice; keep intact all notices stating that this License and any non-permissive terms added in accord with section 7 apply to the code; keep intact all notices of the absence of any warranty; and give all recipients a copy of this License along with the Program.
If GitHub then uses the source code in a way that violates the license, there is no provision in the GitHub terms of service that would allow GitHub to deflect legal liability to the GitHub user who uploaded the program. The uploader satisfied the requirements of GPLv3, and GitHub would be the only party in violation.
I'd like to see that theory tested in court. Section D3 of the terms says:
> If you upload Content that already comes with a license granting GitHub the permissions we need to run our Service, no additional license is required.
and section D4 does not mention any permissions that GPLv3 does not already cover. GitHub automatically recognizes when a repo is GPLv3-licensed, so it cannot claim ignorance of what GPLv3 is.
> You may convey verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice; keep intact all notices stating that this License and any non-permissive terms added in accord with section 7 apply to the code; keep intact all notices of the absence of any warranty; and give all recipients a copy of this License along with the Program.
https://www.gnu.org/licenses/gpl-3.0.en.html
If GitHub then uses the source code in a way that violates the license, there is no provision in the GitHub terms of service that would allow GitHub to deflect legal liability to the GitHub user who uploaded the program. The uploader satisfied the requirements of GPLv3, and GitHub would be the only party in violation.