Amtrak Car in Rocket ?

Hello, I am a Japanese and trying to model Rock Island trains in 1960s - 1970s.
Recently I watched previews of Greenfrog video "Rockets defy discontinuance" and "This was the Rock Island" on youtube, and I found one Amtrak car next to Big Ben in the consist of Quad Cities Rocket in 1970s. I believe that is a Diner, but I wonder why that is in the Rocket ?
Does anybody know why ? Do I take other equipment for Amtrak car ? I will appreciate any answer.
Thanks.

The Rock was out of money, so occasionally an Amtrak car was leased when there was no diner left or repairable. I've seen the same thing in pictures.

STSHNY:

The car you saw in that Green Frog video, with the Amtrak "phase II" red white and blue striping may or may not have been a car leased from Amtrak to substitute for an out of service Rock Island car. It may have been a privately owned car, just as the BIG BEN was a privately owned car. During the early to mid 1970s, Amtrak required private cars to be painted in Amtrak colors if they wanted to operate in Amtrak trains. Later, they relaxed this requirement to just having the red white and blue stripe on the side of the car, and finally they eliminated this requirement completely. So, it is possible that a private car was operating along with BIG BEN that day, in the consist of this Rock Island passenger train. I looked closely at the video and could not find a car number on that car, although it does look like a Budd built dining car.

I regret that I never rode the Rock Island's Peoria and Quad Cities trains, or the D&RGW Rio Grande Zephys during the Amtrak era after May 1, 1971, but at least I did ride the Southern Railway's Southern Crescent and the Georgia RR mixed trains in 1977.