Anything can get hacked, especially with crimes like this on the rise in the crypto world. But honestly, $4 million might not be that huge for them- it could just be part of their daily transactions since withdrawals are automated at this casino.
A good casino can always cover its losses, from its own money or with a quick loan. I don't know if $4 million is a little or a lot for this casino, in any case, it's good that they covered it and showed that they are serious about what they do.
The CEO already said that they have covered what has been lost in the hack, meaning it's from their own money. I'm seeing that this casinos has been in the crypto space for years and they have a lot of promotions and competitions paying huge amount. So it's safe to assume that it might be just a drop in the ocean for them.
I agree with you that anyone can be hacked, even easier if they have an insider. With hacks this big, I always suspect that someone from the inside helped... I doubt we will ever find out, we never get the whole story in the end because of security reasons. In any case, I hope they manage to get the money back from the hacker... sometimes it is possible if the hacker makes a mistake.
Hopefully it's not a inside job because it's going to hurt even more. When you trust your own people to run it for you but then they've been thinking of stealing from you, that is frustrating. Hopefully, in the name of justice, they can recovered at least some part of the loot as the criminals have deposited it to CEX.