Unless you work for a financial institution and actually know otherwise, I actually don't think they did either. Three different employees of the financial institution all gave me a consistent answer. They explained an Interac etransfer isn't a transaction between two financial institutions, the transaction is from one institution, to Interac, to the second institution. The reason for not sharing information is security, your account information isn't exposed to the internet and isn't shared between the sender and receiver or the institutions involved.They are either incompetent, or they lied to you. Once the etransfer is claimed, the banks on both sender and receiver side have the banking information (bank, account number, legal name of the account holder).
Anonymity was never promised as a part of e-transfer service. Exactly for the reasons of fighting money laundering, banks have to keep those records.
Moreover, to my knowledge, there is no legal reason why a bank cannot tell you who was the counterpart of your own transaction. The clerks may not know how, or they won't spend the time, but they have it. They can find the information if it's subpoenaed, for sure.
It's possible your setup is safe, but I'd warn others that bitcoin and other digital currencies transactions are not as anonymous as they may appear, either. Lots of extra steps are needed for that. Blockchain technology is like a ledger, after all, and can link a money transfer to an identifiable transaction like buying coins on an exchange. Many people got letters from IRS and other tax agencies that demand explanations on those transactions.
For bitcoin, my understanding is you are wrong. Yes the blockchain is a public ledger of transactions between bitcoin addresses, but the identities of the bitcoin addresses start anonymous. As long as you only use a bitcoin address once, and move your balance through mixers, which combine transactions, to newly created addresses, it becomes impossible to trace. That is how funds that have been extorted through ransom demands for data recovery or stolen from exchanges get 'lost' on the blockchain, and the identity of the extortionists and thieves remain unknown. Otherwise when the Japanese exchange Coincheck had $400 million stolen from their exchange wouldn't they have just arrested the perpetrators?