As you say, it sounds like he's trawled the CAA registration database, and intentionally or otherwise, he's sailing fairly close to the wind with regard to trading standards legislation.
While he's not actually sending you an invoice for services rendered, he is implying that you should provide him with your financial details for previous or future payment of bills. Unless you have entered into a specific agreement to do so, i.e. a continuous authority payment from a credit or bank account, he cannot legally send you any bill or deduct payment if you don't owe him anything.
Under the circumstances, it sounds extremely dubious.
Don't reply and refuse to negotiate with him or any part of his operation.