Watch the video, which cites sources (https://drive.google.com/file/d/0B2p-HoK9KXEAamNTTkdSaERqdGc...). This isn't just staff active on the train, but maintenance, administration, back office, etc.

Amtrak employs ~20,000 people. When you get to the number of annual passengers, and how many trips they operate a year, it breaks down to ~4 passengers per employee per trip.