Could be for a wide range of people. Can you narrow it down, a station you were at perhaps? Were they wearing any uniform? Did they have a pass around their necks?
Even by narrowing it down in this way however it still may be very difficult to pinpoint who it was.
You could go back to the station and ask the Supervisor who they were, or if there was any record in the station log book. But this would only be successful if they were authorised to be on the station and not just passing through in an ad-hoc manner.