Hang on. Isn't his argument here that the case should be dismissed based on the PRA?

Yes. Trump is arguing that the PRA creates an issue at law that prevents the case from moving forward. Issues of law are decided by the judge - whether it’s a jury trial or not. So if the documents are “personal records” as a matter of law, because they are exempt from review, the judge can (and should) decide that question before the trial.

If the judge decides that the documents are not exempt from review, then they are back in play to serve as the basis for the crime that was alleged. But the body that conducts the review would be the jury, if that is a question of fact.

Many (most?) trials involve intertwined questions of fact and law. Depending on the posture of the case, sometimes one side can win on the law alone, while the other side needs to prove both their legal and factual argument.