I thought the law actually said follow instructions during the conduct of their normal duties. A FA couldn't order you to stand on your head and then have you arrested for disobeying. In this case, I think the root question would be whether telling pax to put their hands on their head was part of the FA's normal duties.
But ... I can't find the actual law offhand.
Crew members, maybe (within reason). LEOs, nope. If they suspect me of a crime, they can detain and arrest me. Otherwise, I am free to go.