I think you are missing a bit:
1.1. Purpose and scope
The purpose of this Certification Memorandum is to provide specific clarification and additional guidance for certification of equipment and devices intended for use in operations involving carriage of human external cargo on helicopters by means of cargo hook or hoist.
A harness used i.e. while filming usually is not tied to a hoist or cargo hook, is it?
Therefore (imho) somebody still sitting on the floor inside the helicopter would not qualify as HEC.