Hmmm. I hope this doesn't cause issues for those of us who download Youtube videos to watch locally.
isn't that a criminal offense already?
Criminal offense, no.
Civil lawsuit, yes, probably, especially if you agreed to their terms of service.
Criminal offense or 'legal action' is propaganda many media companies use to put people off piracy and whatnot. But in reality, it's a civil law case at best (happens more in Germany). Most of the times they can't do much other than block your IP and send messages please not to do it again.
Don't forget that for YT/Google, every user is a breathing data node ready to be mined, so the worst they can do is get people completely off their (advertising) platforms/reach.
There are only a few cases where piracy is really illegal by criminal law, that can put you in jail. Think software piracy, computer crime, etc.