You used a Google account to login to some Google app on iOS and even after logging out of or deleting Google’s apps the login prevails? Yes, Google’s apps magically remember used accounts.
Actually, it’s not magic, but most likely the logins are stored in Apple’s iCloud keychain. That means they will persist for this iCloud login and even appear on all devices where this iCloud user is logged in to. Quite annoying, especially if you don’t want to link different Google accounts because of privacy reasons. But there is an easy albeit not entirely obvious way to delete the stored Google logins.
Installing Gmail gives the option to remove a login from the account settings page in Gmail iOS on either iPhone or iPad. By doing this all logins will be removed from all Google apps including YouTube, Google Maps, Google Chrome and others.
To remove a login tap Accounts > Edit > Remove for all the logins you want to remove. Removing a Google login from one app deletes it for all installed Google apps on this device.
The same goes for Google Drive, Google Hangouts and Google Calendar. These apps can manage accounts more thoroughly than the rest of the Google apps. Maybe Google will enhance the other apps in the future as well.
It took me some time to figure this out as I didn’t have one of those apps installed on my devices. The Google apps I used and where I wanted to get rid of the accounts don’t have this ability.