Resisting arrest means you haven't been arrested yet. If he was already under arrest then he couldn't resist it. He was being detained. If he were under arrest

Resisting arrest means you haven't been arrested yet. If he was already under arrest then he couldn't resist it. He was being detained. If he were under arrest then there's procedure to that which has to be followed. But while being detained if one were to be argumentative then it could change from being detained to being under arrest, which then resisting arrest comes into play. But that's just arguing over semantics that typically don't come up at the court hearing. People get charged with non-relevant crap all the time to trump up the charges.