1 Bit = 100 Satoshis
So in this case, 100 Bits being the max bet was worth 10k Satoshis (BTC0.0001) bet and 3k Bits was his website's entire bankroll = 3,00,000 Satoshis (BTC0.003)
I was amazed to see how a person can promote his website without complete details about his bonus promo (didn't tell in OP that it was a one-time-use code) and then came the bankroll size which was a joke. He must have told us that he is "testing" his site's vulnerabilities and exploits before launching fully or who knows if he's got that 3k bits only in the website's bankroll!