There is actually a big difference if the casino has no restriction on withdrawals of someone which deposit/s is unconfirmed. Imagine if a player wins with their unconfirmed transaction, and they'd be able to freely withdraw said winnings. This player could also try to double spend the same UTXO with a much higher fee so it will likely confirm first making the previous transaction invalid.
I don’t think that’s possible. Back in the early days of casinos and sportsbooks, I experienced them crediting my deposit right away as long as it was already on the blockchain. But they wouldn’t process the withdrawal unless it had at least one confirmation, which I believe is just a standard security measure.
You misunderstood. See the person I quoted saying "There is almost no difference if the gambling site does not allow withdrawals before the confirmation. In this case if the user use double spending then there will will have no benefit of the user."
Thus, the bolded bit was an example risk if a casino does not impose restriction on withdrawals of folks with unconfirmed deposits. There is a difference as you do open the platform for abuse if you don't have it, and bad actors could surely benefit.