Hope you can give him something good in return to find your unnotice bug
Yes, for a bug bounty.
Bug bounty compare to his winning, this is not enough. Usually bug bounty is only some amount and that is not much and i think that should give him at least half of the winning prize. 10 btc is good amount to win with recent price. And like i said before this is not his fault that he can bet that huge amount
I know, right? If he got paid for bug bounty, it's better than nothing. I doubt admin will pay him although for 5 btc (half from his winning amount).
Reached 10 btc from only with 1000 satoshis is a really awesome, also he did that on crash game. Maybe he can win lot too in bustabit.