Originally Posted by
enpremiere
Speculating here but it could have been a flyer who had purchased the American Airlines Five Star Service / FSS and the agent was actually an AA premium agent pre-boarding them. IIRC you can request to board ahead or after the crowd.
Seems like a logical answer.
I don't think I've ever seen a case where CK were invited board prior to pre-boards. Usually pre-boards, then CK, then group 1.