The hands on head, no recording, and deplaning away from the gate suggests that there was a threat to the safety of the aircraft by the person who was ultimately arrested.
The regulatory requirement for compliance with crewmember instructions comes from
14 CFR 121.571 (a)(1)(i),
"... This briefing shall include a statement that the Federal Aviation Regulations require passenger compliance with the lighted passenger information signs, posted placards, areas designated for safety purposes as no smoking areas, and crewmember instructions with regard to these items. ..."