FATCA is a mess. For example, some non-US (e.g. Hong Kong) bank will assume you are a US person (and presumably share your account info with the IRS) if you opened the account with a US phone number unless you prove that you are not a US person by doing some troublesome paperwork. (So what if you have a US number? It could be a Google Voice or Twilio number.)

The onus should be on the IRS to prove to the bank that the account holder is a US person, not the other way round. They want the money but they won't do their share of the due diligence.