The buck stops with the user, when they use code from any source at all, whether it's their head, the internet, some internal library, lecture notes, a coworker, a random dude of the street, or who knows what else, it their own responsibility to ensure the code they're using has been released under a license they can use. They don't get to go back and point fingers just because they didn't do their own due-diligence.
The exception would be if a vendor provides code under a legal contract providing liability and an agreed license, that has not happened in this case so there's no reason to expect any legal protections.
