It seems rather unlikely a priori that all users of an exchange would be involved in this, but as they say it seems to be the case. I guess it's bad wording if it's not a scam.
Recently, the platform users' funds were involved in 'money laundering' and BKEX is currently cooperating with the police to collect evidence, for which we will suspend withdrawals to cooperate with the work.
Either way, this is bad news. If it's a scam, because of the damage to those affected and adding another to the list of scam exchanges, while if it's real money laudering and more continue to be added to the list over time, I think we will eventually have regulations banning mixers and being very strict with exchanges.