That's not actually what the FBI did. Without discussing their idea with Apple, they decided they'd try changing the AppleID password associated with that iPhone, ignorantly thinking that would somehow get them access, so they had the San Bernardino County Health Department IT guys to log onto Apple and change the AppleID password. Had they NOT done that, Apple could have forced the iPhone to back up to any WIFI to which that iPhone had been previously connected, but by changing the password, they broke the link.
That leaves the only means to get in is to break the passcode.
Thanks for explaining.