I think that the reason can be, because your bet is too small to be counted for Competition
No, the bet was exactly 1% of his current bankroll, and was accepted.
The bonus given per bet is now 13% of the wagered amount. As for the rest, I think it all checks out: you made a bet with 0.001 BTC, at odds of 2.4, and won 0.00253 BTC (that is, you spent 0.001 BTC to place the bet, and received 0.0024 BTC + 13% of the original amount, or 0.00013 BTC) - so, you end up with 101.53 mBTC.
Yes, I see now, that was his 1st bet