If 30 is what seems safe to him, who are you to argue?
If he's not following the law, then... anyone? Everyone?
Highways do have a minimum speed though. 80kph here.
California's highways have a minimum speed, too. It's "drivers cannot drive so slowly that they block or impede the normal flow of traffic". So if he's going 30, and everyone else wants to go faster, he's breaking the law. Also, California state law requires that if you are on a highway and there are five or more people behind you, YOU MUST PULL OVER AT THE FIRST SAFE OPPORTUNITY TO PERMIT THEM TO PASS. This is an extremely underappreciated and underenforced law. I've seen someone pulled over for it just once, they were operating construction equipment and there were dozens to hundreds of people stuck behind them — I could not see the end of the line, so I only know about dozens.