No but the beauty of this is that Nvidia is absolutely going to deny this and in order for them to get someone to prosecute and show proof that Nvidia hacked them back they would have to turn themselves over for their own crime which they obviously aren't going to do.

At which point does a hack become criminal?

Probing defences? Breaching defences? Accessing your own, stolen data? Downloading it? Downloading everything else?

If I see the guy who stole my car, nick the car keys from his pocket and drive off, is that theft? What if my car also has his wallet, and I drive off with that?

Not for want of making it legal. The Active Cyber Defense Certainty Act (ACDC) has been proposed to the House of Representatives several times. It would make retaliatory hacking legal under some scheme. It has never made it out of committee.

In US terms, that means one or a small group of Representatives (in this case 18) proposed such a law. It got referred to the subgroup in charge of vetting proposed laws in that specialty area (in this case the subcommittee of Judiciary called the Subcommittee on Crime, Terrorism, and Homeland Security). From there, he wasn't able to convince them to even green light it for a full vote in the House of Representatives, let alone going to the Senate or becoming a law.

No, but who's going to prosecute?

The hackers attributed the reverse attack to NVidia but where's the proof? I doubt NVidia is going to put out a press release (if they committed the alleged act.)

What's the ransomware team going to do? Complain to the authorities? Sue?