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.
Google is a lot of things for a lot of reasons. This isn’t one of them. There’s plenty of reasons to bash them without needing to pull shit out of one’s ass