Asides opening multiple accounts in a casino, what else can cause it because the gamblers are always claiming that they do not have another account, and the casinos are not always providing proof of the other account when they make the accusation.
other possibilities of being accused of multi accounting are, using a VPN, using someone's device, using someone's internet, using a public wifi, using computers in an internet cafe, transacting with a wallet address that belongs to another gambler in the casino, etc...
The things I mentioned are the ones I've seen posted on the scam accusation board over the years as possible reasons for being accused of multi-accounting.