Was he under arrest or bring detained? My understanding is that as a US citizen he committed no crime and could have asked if he was bring detained, under what

Was he under arrest or bring detained? My understanding is that as a US citizen he committed no crime and could have asked if he was bring detained, under what law, or if he was free to go... However, through coercion, and lack of knowledge on his rights he consented to this interrogation. Anyone know for sure what his legal position was?