That is the unlock screen, it has nothing to do with Google. It's whatever PIN you set up to unlock the screen.
If you don't know it, you'll need to plug phone to PC/Laptop and boot it into recovery mode to factory reset then set phone up again.
When you do this, if you're logged into your Google Account you'll need to confirm the email and password for that to set phone up again.
I believe Google backs up device settings so if you've backed up to Google and restored the back up via set up process prompt then that's why you have the lock screenpin.
To get into recovery mode
Plug phone to PC/Laptop
Press and hold volume down + power
Once phone turns off immediately press and hold volume up and power
If boots into recovery
Press volume down to highlight factory reset and press power button once
Use volume down to highlight option to confirm the reset and Press power button once
If successful it'll ask you to reboot system not. Press power button once to confirm and wait for phone to go to welcome screen and set up again.
If it does prompt to restore data from Google then skip it so don't get the pin lock back on
