According to the FAQs, they do not ask for any documents or verify KYC, so no documents will be requested if you win a large amount.
But based on Terms, the casino also reserve the right to ask KYC when a player reach a certain threshold so there is still possibility to be asked for KYC for large amount of money.

However this is a common term related to KYC and all players should be ready to conduct KYC at anytime when a casino clearly has this terms.
Not only for large amount of withdrawal but it can be for any other reason if the casino think that a user need to be asked for identity verification.