I would ask them to show proof of funds to show that they can actually pay out 19k Bitcoin, which they clearly do not have.
It's actually the jackpots from the game providers they use. Play'n'Go for example provide them with a game that has a jackpot of around 10 Bitcoin.
This would be a jackpot available to all sites, Bitcoin or Fiat, that use Play'n'Go games.
What they seem to be showing is the total of all the jackpots across all games and providers that is pooled from many sites using these providers.
You would not actually be able to win a jackpot of 19k Bitcoin on their site.
Yes that's the only real way to do it but I want to add to what you said and say that just because the can do something doesn't mean they will. I dont think I would ever trust anywhere with a lot of btc. Unless it's a lot for me but only a small % of the bankroll if its a really large bankroll. I know sometimes for be winsnthey have to wait so they can draw out the cold wallet.
