Audio problem: Edward has Thomas' whistle sound when he first sees Trevor and when he approaches Wellsworth Station.
Continuity mistake: When Edward stops at the station, a close up of his whistle shows the sky is sunset dark, but when he arrives, it's bright daylight.
Visible crew/equipment: When Edward sees Trevor for the first time, the edge of the set is reflected on Edward's boiler.
Answer: He was in the water.