It’s a real feature in first party apps (messages, mail, etc), but it’s not fully automatic. When it thinks that a number/address/etc is related to an existing

It’s a real feature in first party apps (messages, mail, etc), but it’s not fully automatic. When it thinks that a number/address/etc is related to an existing contact, it’ll prompt the user to confirm or deny, and upon confirmation the info is added. Ultimately it’s up to the user.