I haven't checked the stats on this yet but I wouldn't be surprised if they took a bunch of bets prior which were all loses and their win isn't exactly a full 2 BTC.

Usually when there is a large win like this with very small odds of winning the gambler has been placing bets for a while and they are either at break-even or sitting at a small loss.

I have tried to bet like this before and usually if I am betting at 1% win chance, I would take almost 100 bets and they are all losses and when I finally got a winning bet, I would just quit. I think this strategy works best if you win somewhere in the first 25 bets or so and then you got a better edge.