Even in their sites, they have fans who try to impersonate fake winning claiming it was the online gambling sites that predicted the games for them.
It is all lies just as you said, they are edited game slips just to attract the audience with the evidence of those forks backing them up with fake testimonies of their 100% sure prediction as experts.
as already said, they could be people who are paid or employed by the casino to promote or get more new users. I saw this kind of thing on Telegram channels where they usually broadcast live some matches and also offer VIP groups for predictions. They even offer to help create an account and teach beginners to bet on the sites they recommend.
Maybe at the beginning, the prediction given can be accurate, but after that, it will only provide a very small prediction accuracy.