He never left the scene, charges were never filed, a warrant was never sought for his arrest that we know of. He was not arrested. He was detained.
He answered questions, so we know he participated in a custodial interview. No way did they not mirandize him if they believed he was potentially involved. If they provided him advice of rights, he then necessarily waived them to participate in the interview. He could have requested to stop talking without an attorney at any point. Catch is, they’d just have to stop talking to him. He’d still be detained on scene until the search was done.
JMO