Passkey is some sort of specific unique key to a device allowing to use a pin on a device instead of the password. But which won't work on another device.
Now I don't know if that key can be stolen or not, or if it's really more secure or not, as people have really unsecure pins.
And it's expected as you still had that device. And it's not the same key, a new key has been created for that new device. Now if that device cannot be accessed?