Emulation is legally protected both explicitly and through legal precedence. The replication of APIs for compatibility purposes has been argued to the US Supreme Court and found to not be copyrightable. At least within some pretty broad scope.
IANAL, but I fail to see what legal basis Nvidia is relying on. For a single user or company who owns no Nvidia hardware this feels moot. For a company with existing Nvidia hardware I could see them having an argument, kinda. But wouldn't that be squarely in the anti-competitive behavior wheelhouse?