Well, if I had to guess, I be more inclined to think it may be an ex-CB&Q diner, since Amtrak still has a number of those running around, in the 1800 class.
It's Amtrak owned, even has their paint scheme on it. I just didn't catch the car number, so I don't know the history on it. Looks like an ex-ATSF car to me...