Your bank account number is by design semi public knowledge. Every check you have ever written has it at the bottom. It was never meant to be private.
What's your source on that? As far as I know, Regulation E generally requires banks to make good on errors in electronic fund transfers (including ACH transfers for which the customer is not liable) within 10 days of being notified. That can be in the form of a provisional credit while an investigation is ongoing, though.
The numbers on the bottom are the routing number and account number of the payer. Anyone can make and sell them, and anyone can buy them.
It's not a complete guard, but it does prevent ACH attacks.