More to the point, they were involuntarily checked even though the OP was within allowed baggage limits (i.e. per OP's comments, they weren't trying to carry extra bags into the cabin).
I know I go to this well frequently, but would a chargeback/contesting the (presumed) CC charge be worth pursuing (taking the attitude that, in a pinch, ANA should take this out of AC's hide)?
And...well, let's just say that we're back to the fact that I would very much like to see rules requiring short gate-checking/gate pickup at the end of a segment (a la "pink tagging") to be allowed. Not gonna happen, but it would be nice (especially if I'm trying to avoid dealing with a clumsy ticketing situation and/or an airport with a bad baggage terminal).
(Also, I can definitely read between the lines, but the degree cultural misconnect between the Japanese corporation's phrasing and how it would come across to a regular, irate North American traveler is impressive.)