<snip>
I believe he doesn't use his money betting that big

It doesn't matter where the money came from, it's still his. He could've taken it off the platform at any time, but he chose to keep gambling. It's all part of his strategy. He bets big to constantly win daily jackpots and other prizes, which give him a much higher return-to-player rate compared to other players. Plus, he gets a ton of rewards points for betting such large amounts, which is just an added bonus.
Being a "whale" sure has its perks! You can bet big, win big, and earn even more rewards points, which can give you an edge over other players. It's a pretty sweet deal if you can afford it!
yes, because the game on freebitcoin is just rolling the dice and of course playing the roll of the dice there is no other technique besides martingale it's just that this kind of technique requires large capital, maybe if I were him he would of course do the same thing as what he did