From this link "Not every violation of the rules will lead to an account closure. Just because an account is shared does not mean the account will be blocked, and if a shared account is not blocked at a particular time, it does not mean the sharing is allowed.". Basically the staff can decide to ban or not. It's against the rules but it's not an instaban the staff can decide what to do for every report they get and "The rule is there to protect the account holder, not to punish. The rule is also there as an supplement to other more serious rules – for example, account sharing cannot be used as an excuse for some other rule being broken.". So more or less 100% staff decide and they can even not ban.