Lol, just because he's giving a perfect description of it doesn't mean that he has experienced this lifestyle. There are several stories and documentaries that can tell you how these things are... gambling in prison can be very different because they don't have access to money, it's of no good to them when they don't have freedom, what they put on the line might be smuggled drugs, their lunch and even a bed space
I have heard that prisoners use cigarettes as their currency in prison. Also some prisons have
shops inside. Prisoners dont have cash, but they have money on balance. Mostly prisoners use shop to either buy food or hygiene products. Btw, did you know, that prisoners earn while doing
prison labour? Extremely low, but still they have got some money. Money gives them variety of opportunities and things to do in prison.
At the same time, it is often better not to get involved in gambling with prisoners, since it is better for a newbie to stay away from the card players there. There is so much free time in prison that the card players there are very good at playing cards, and they can cheat, and also their cards are dishonest, with marks.
I think they specifically say first: "let's play for fun?" And then they try to get the newbie excited, after which they will try to win everything he has.