Acela 2253 originates in Boston and crew changes in New York. Penn Station New York is notorious for keeping boarding passengers milling about in the lobby until the train has already arrived and detraining passengers have cleared the platform. The outbound crew would be on the platform to meet the inbound train and would see passengers leaving the train and others with their seat checks remaining aboard. When the gate announcer sent the herd down to the wrong platform it would have been nice if the outbound crew had noticed no one coming on board and called for instructions.