Who is this user and what actually happened? I believe we should hear his/her side of the issue. That situation might be something to learn from if our accounts, despite being innocent, might have the same issue. Can you post the links of his posts?
There are many such cases. Let me just list the 3 recent ones, and all have been resolved in favour of those accusing the casino.
1.
https://bitcointalk.org/index.php?topic=55287562.
https://bitcointalk.org/index.php?topic=55353353.
https://bitcointalk.org/index.php?topic=5530971Do you believe that they are merely guessing?
I think they are, or their flagging system has a lot of false positives. Reason being, after telling the user to list all his other accounts, they eventually unlock the blocked account if the user insists over several days or weeks
He/she should also ask them HOW they made the absolute conclusion that he/she has more than one account.
Those are the methods casinos don't disclose, but at least they should be able to list to the user the accounts that are linked to his instead of asking him to list them.