The code I read to them was a Google account recovery code. That’s how they accessed my Google account. I, mistakenly, believed they needed to confirm I was still alive and the rightful owner of the account.
Then the attacker used Google SSO to perform the initial log in to my coinbase account. Then they opened Google Authenticator, signed in as me, to get the coinbase auth code so they could complete coinbase’s 2fac.