Yes absolutely the fault of the sender, because is clearly stated in the casino terms and conditions that deposits via wrong coin network is a lost for the depositor, but in few cases we see that gambler's get lucky that the deposits with wrong network or coin as far as the coin and address is the casino valid payment details their treat is as mistakes and credits the gambler accounts with the right amount.
In such cases, the depositor's money is usually not refundable. Because the casino rules are very clear about this. Where the depositor is responsible for the loss due to the mistake, the depositor will have to take responsibility. But I would not be surprised if a casino suddenly returns the money. I personally once sent money to the Ether chain instead of the BSC Smart Chain by mistake, but I was lucky that I found the money. It was returned to me. But if they did not give me the money, then there was nothing I could do. I will be responsible for my mistake.