That doesn't seem to be the case here; they're suing him in a federal district court in CA, and you can't sue people multiple times for the same thing in different federal district courts, since the federal court system is considered one unified system (just with administrative divisions). It's more with state law that you can try to pursue multiple suits in different states, since the state court systems are independent from each other. But most (all?) states don't have state-level law against circumvention; if the suit is relying on the DMCA, it has to be in federal court.