The casinos may pay those who promote online casinos to attract more people to their casinos. People who see the stream may not know about it and end up visiting the casino because they see the streamer can easily earn money. They think that they can also earn big winnings.
It is obvious, when a streamer and a casino had a deal, the casino will provide the bankroll while the streamer promote the gambling platform. Streamer even flash their affiliate link to track people who signed up under them. This is also one way for the casino to determine if the marketing is a success.
He may just want to ask our opinion about whether it is fake money, money from referrals, or even his own money. We don't need to know that; what is certain is that we are playing with our money. And if we lose, it's our money.
I think we must know the facts behind the streamers' bankrolls. Because more often than not, those who are watching the stream will try to emulate the action of the streamer. Knowing that the money used by streamers is sponsored, then the idea of viewers imitating the streamer will die down.
My rule of thumb is that most of streamers use fake money or a mix of actual funds and bonuses provided by the casino.
If the streamer favors an specific casino over others, it would be easy to assume there is some deal going on behind the scenes, it is the same with those webpages to gamble with Counter Strike skins and cosmetic objects. I have read about cases where very popular youtubers record themselves gambling on platforms they personally ownership over, of course, they do not disclose this fact to their viewers.
True, if a streamer favors a casino or always plays on the same casino in his stream, there is a huge possibility that the streamer is sponsored and that the money he is using to wager is from the casino and not from his own pocket. Those who are not sponsored by casino will play in different casino in order to search for his lucky platform where he can win easily.