I don't know how safe or how risky this casino is but what the support explained to you is really correct. Before joining any casino it is important to know the rules of that casino. Since your fund size was $10 this loss won't hurt you much, but you have done a good job by opening this thread which will encourage other gamblers who do affiliate marketing to read the rules carefully. Because when you break the rules the casino will have more excuses not to pay you out because they are legally correct. But yes, the owner treated you rudely, this makes me think twice before joining this casino.
Inactivity
After >52 weeks of inactivity, accounts may be deactivated or suspended.
Volatility
Crypto funds that have not been used to wager/play for more than 6 months, and increased in value (since added to the account/date of transfer) by more than 20x, cannot be withdrawn.
Source: https://sharkoin.com/terms-and-conditions/