I caught a mention in all of my readings today that there is apparently a Kerry backer swift boat vet who works at the Vietnam embassy in DC ( something like that )...seems that any such trip to this village would begin there.
It would be impossible that one of the good SBVs made a voyage there without Kerry ( and then ABC ) knowing exactly who that guy is considering all of the documentation that it would require to make the trip and realizing that Kerry owns that access since he was able to place a bouncer/ID checker at the door.
Sounds very possible to me that the Kerry people gave the village a "prep" with the mystery man and it's at least possible that Koppel has been duped to some extent which would be easy since his sympathies already slant toward wanting to believe.
Koppel need only ask the Kerry people who the "mystery man" was and if there is no answer he should have the integrity to realize it was a Kerry operative.