As a military veteran the guy might have had some misplaced respect/trust for police officers previously.

His consent wasn't likely to be required. That consent is merely a superficial layer, easily discarded by staging dog alerting. If the guy didn't consent out of misplaced respect, he may have chosen to do so because he realized the cops can get in your car if they particularly want to no matter what you do. And once he mentioned the large amounts of cash, that was that.