It's not just where the money is coming from but whether the odds are different from regular players. The gambling sites who sponsor this can very well adjust the odds per user so that the streamer gets consistent wins where as real players get the real odds which favor the house.
I've seen such gambling "ads" on YouTube, obviously they're not presented as ads nor even as gambling, rather they're presented as a way of making money, a loophole in the game, all the way to saying that there used to be an old version of this game but they closed it down due to many people winning, but this new game also has a loophole (how convenient!). In the "ad", they were consistently winning, in such a way where there's basically no way to lose even if you tried it on purpose. I very much doubt the video was falsified, rather the gambling platform was able to change the odds per-use so that their affiliates can get consistent wins so they can promote the platforms without requiring video trickery.