An old OS knew my current wifi password automatically

I connected a system stored on an external drive into a new laptop and booted it up. Upon logging into the old system my new WIFI connection logged in automatically without a password prompt. My laptops harddrive is encrypted and I wasn't mounted yet. I checked the logins and the old system hadn't been logged in since I moved to this new place.

Do WIFI passwords get stored outside the harddrive? I know the Bluetooth connections are stored on the chip itself and there's a special key command to administer the chip.