Just because someone bets big on a gambling site isn't enough evidence that they have a sufficient bank roll.

They could of easily send those BTC back and forth and made those bets.

This is no different than with happened with MtGot with that robot that they had. It kept buying hundreds/thousands of BTC everyday and everybody assumed they had a huge bankroll because there was volume.

But in the end what happened? The bot was buying unlimited BTC and paying exactly $0 for each trade and eventually the website imploded.