Tracked down an interesting post on the subject:

RulerOfPersei81.7k points
7 days ago
I work in the banking industry, and this is a well known issue. Here is what likely happened: the shop owner was depositing too much cash or moving cash around multiple accounts with multiple owners. This forces the bank to file suspicious activity reports (SARs) and eventually close the accounts. Here is the kicker: the bank cannot disclose to the account holder why they closed the account, and there is a penalty with the possibility of prison to the actual employee that discloses this to the account holder. This is literally the law in the Bank Secrecy Act.
Even if the bank wanted to tell the customer, unless there is an employee willing to go to prison for it, no one can actually tell the customer why their account was closed.