As Brian rightly says, under the Posse Comitatus Act unless the full Insurrection Act is invoked (which it hadn’t been) it is strictly illegal for marines to arrest or detain anyone. It literally does not matter what this person did. It is illegal for a Marine to do any detainment. California has citizens arrest laws that allow citizens to detain someone (with reasonable force) while waiting for police - but due to Posse Comitatus and UCMJ these do NOT apply in the same way to the Marines. Any use of military equipment, military authority, any claim of jurisdiction, any one commanding the Marines to do this, or the Marines giving any command to the person that would be perceived as a legal order, make it a violation of the act and an illegal use of the military!