If he did so, then maybe he has violated the rules but I don't know if same rules apply for every casino but I was a victim of such circumstance but mine was a crypto casino by the way, it was just a local based online casino here in my country and the reason for me having multiple account was because I lost the previous mobile used for registering on their website and in other for you to make certain amount of withdrawal an otp verification must be sent to that same mobile number used for the registration.