I don't use the Chrome user account features and don't want the browser to know my Google account. In the past I just didn't sign-in to Chrome, signed-in to Google (mostly to sign-in to StackEchange with my Google account) and it seemed Ok. But now as I've updated to Chrome 69 it signs me in to Chrome every time I sign-in to StackExchange with my Google account. Can this behavior be disabled?
As you noticed, starting with Chrome 69, this “auto sign-in” feature was added. It automatically signs you into Chrome when you sign into a Google website or use a Google account to sign into other websites (e.g., Stack Exchange).
This feature was frustrating for many users and since Chrome 70, users can disable it:
Open settings and search for "sign-in".
Disable "Allow Chrome sign-in".
To apply this change, relaunch Chrome